Exchangeable cation (Mg) swell potential reduction method

ABSTRACT

A method of reducing the swell potential of an expansive clay mineral. The method includes (a) carrying out a forcefield-modified molecular level simulation to determine an amount of a swelling reduction agent to be incorporated into the expansive clay mineral to form a swelling reduction agent incorporated expansive clay mineral with a reduced swell potential Si(ECM) that is no greater than a pre-set level T, wherein the swelling reduction agent comprises at least one cementation material of calcite, gypsum, and potassium chloride and/or at least one exchangeable cation of K+, Ca2+, and Mg2+, and wherein the forcefield-modified molecular level simulation comprises molecular mechanics, molecular dynamics, and Monte Carlo simulation techniques configured to simulate the reduced swell potential Si(ECM), and (b) incorporating the amount of the swelling reduction agent into the expansive clay mineral to form the swelling reduction agent incorporated expansive clay mineral.

CROSS-REFERENCE TO RELATED APPLICATIONS

The present application is a Continuation of Ser. No. 15/933,060, nowallowed, having a filing date of Mar. 22, 2018, which is a Continuationof Ser. No. 15/177,872, now allowed, having a filing date of Jun. 9,2016, which claims benefit of priority to U.S. provisional applicationNo. 62/387,166, having a filing date of Dec. 23, 2015, the entirecontents of which are incorporated herein by reference.

The present disclosure incorporates by reference in its entirety thefollowing thesis: Molecular Level Modeling of Natural and CompactedExpansive Clays, 2015, by Habib-Ur-Rehman Ahmed, King Fand University ofPetroleum & Minerals, Dhahran 31261, Saudi Arabia. This application isrelated to U.S. application Ser. No. 15/134,474 titled “Method forreducing swell potential of expansive clayey soil with nano-levelconstitutive modeling,” filed Apr. 21, 2016.

BACKGROUND OF THE INVENTION Technical Field

The present disclosure relates to methods of reducing the swellpotential of an expansive clay mineral and an expansive clayey soil.More specifically, the present disclosure relates to methods of reducingthe swell potential of an expansive clay mineral and an expansive clayeysoil comprising at least one expansive clay mineral with the aid of amolecular level simulation and preferably with a swelling reductionagent comprising at least one cementation material selected from thegroup consisting of calcite, gypsum, and potassium chloride, and/or atleast one exchangeable cation selected from the group consisting of K⁺,Ca²⁺, and Mg²⁺.

Description of the Related Art

The “background” description provided herein is for the purpose ofgenerally presenting the context of the disclosure. Work of thepresently named inventors, to the extent it is described in thisbackground section, as well as aspects of the description which may nototherwise qualify as prior art at the time of filing, is neitherexpressly nor impliedly admitted as prior art against the presentinvention.

Expansive clays are widely prevalent all over the world as one of themost problematic and challenging soils. These soils undergo significantvolume change with the change in the moisture regime, thereby posingproblems to the stability of the structures founded on such strata. Theexpansive clays become highly erratic in behavior especially whenpresent in unsaturated/partially saturated state having fluctuations ofthe saturation levels. More challenging is the fact that foundations ofmost civil engineering structures are generally placed in the partiallysaturated soil zones with a continuously varying degree of saturationwith the environmental and weather conditions. The American Society ofCivil Engineers (ASCE, 2013) estimates that 25% of all the homes in theUnited States suffer some extent of damage by expansive soils and anestimate shows that in a typical year in the United States these soilscause a financial loss to property owners greater than other naturaldisasters such as earthquakes, floods, hurricanes and tornadoescombined. Expansive soils are also commonly present in the Kingdom ofSaudi Arabia and concentrate mostly in the populated cities. Theseexpansive soil deposits present in the Kingdom of Saudi Arabia containhigh percentages of expansive clay minerals (Table 1). High percentagesof the expansive clay minerals result in high to very high swellpotential of these soil deposits (Table 2). Consequently, structural andfunctional damage to the structures of the entire housing complexes byexpansive clays is quite common in several areas of KSA. Empirical andexperimental based solutions and formulae to predict the expansivepotential of these soils have not been able to provide a comprehensiveunderstanding for the various possible variations in the fabric andstructure of the natural and compacted expansive clay soils.

TABLE 1 Mineralogical analysis of expansive clay deposits in the Kingdomof Saudi Arabia (Hameed, 1991). Sample No. Location BH/TP No. Depth (m)Mineral type (% composition) 1 Al-Khars, Al-Hasa BH-9 2.5-2.7 C(50),Q(10), P(8), K(5), I(9), S(7) 2 Mahasen-Aramco, Al-Hasa BH-13  2.0-2.25C(34), Q(16), P(8), K(3), I(31), S(4), St(4) 3 Al-Hamadiya BH-11 1.0-1.3C(35), Q(10), P(8), K(3), I(30), S(8), St(5) 4 Al-Salehiya BH-12 2.4-2.7C(19), Q(19), P(4), K(4), I(47), D(1), S(8) 5 Al-Khars, Al-Hasa TP-7 1.1C(39), Q(11), P(10), K(11), I(19), S(6), St(4) 6 Al-Naathel, Al-HasaTP-11 2.0-2.2 C(61), Q(24), P(6), K(3), S(6) 7 Mahasen-Aramco, Al-HasaTP-11 2.0-2.2 C(27), Q(19), P(10), K(5), I(32), S(4), St(3) 8 HousingArea BH-1 3.8 Q(9), P(9), S(30), St(12), T, I(40) 9 Housing Area BH-31.8-2.1 Q(7), K(<1), S(25), St(10), D(32), I 10  Umm Al-Sahek BH-60.45-0.6  Q(4), K(<1), P(2), S(13), G(11), D(48), I(22) 11  UmmAl-Hammam BH-8  5.6-5.75 C(<1), Q(10), P(11), D(<1), S(39), I(39) C =Calcite K = Kaolinite Q = Quartz I = Illite P = Palygorskite D =Dolomite St = Sepiolite G = Gypsum S = Smectite T = Talc

TABLE 2 Geotechnical properties of the expansive clay deposits in Qatifarea, Kingdom of Saudi Arabia (Dafalla and Shamrani, 2012). Browncalcareous green and Property range for brown clay, symbol (USCS): AlQatif soils CH and MH Avg. min. Avg. max. Dry unit weight, gd, kN/m³ 1014 Water contet, wn, % 15 40 Liquid limit, LL, % 120 160 Plastic limit,PL, % 30 60 Plasticity index, PI, % 90 100 Shrinkage limit, SL, % 9 15Percent sand, % 0 5 Percent silt, % 15 50 Percent clay, % 50 90 Specificgravity, Gs 2.5 2.6 Selling pressure, kN/m³ 200 1000 Swell percent 2 20

Studies of the interaction of clay minerals with pore fluids and theircontributions to the fabric, structure, and macroscale behavior andproperties of clay minerals are critical not only in the fields ofgeotechnical engineering but also in geoenvironmental engineering,material sciences, pharmaceutical sciences etc. See Katti, D. R., Katti,K. S., Amaasinghe, P. M. and Pradhan, S. M. (2011), “An insight intorole of clay-fluid molecular interactions on the microstructure andMacroscale properties of swelling clay”, Alonso and Gens (eds),Unsaturated Soils, 2011 Taylor and Francis Group, London, incorporatedherein by reference in its entirety. Since the emergence of theunsaturated geotechnical engineering, performance of numerical modelingof the realistic volume change behavior of the expansive clays is achallenge for the geotechnical engineers. Consequently, several effortshave been made to develop constitutive models for the behavior of theexpansive soils by performing parametric studies mostly at the macrobehavior level and to a lesser extent at a molecular level. All thedeveloped constitutive models do not comprehensibly incorporate thecoupling of the behavior at the macro, micro, and nano/molecular levels.Moreover, most of the developed constitutive models pertain to thestandard expansive clay minerals compacted under controlled conditions;models covering the natural and real soil fabric do not exist.

Lack of proper understanding and knowledge of the nano/molecular levelinteractions of the clay minerals with pore fluids and the othernon-swelling constituents have limited the development of specificconstitutive models encompassing the accurate behavior under severalpossible combinations of clay, fluid and other non-swelling particles.This behavior becomes further complex for the swelling clays when theinteraction between clay, fluid, and the non-swelling clay particlesbecome predominant.

The swelling behavior of expansive soils is intrinsically controlled bytheir natural fabric and structure. Although the fabric of expansivesoils is quite complex, Mitchell attempted to discretize soil fabric tobe consisting of three general regimes of elementary particlearrangements as single form of particle interaction at the level ofindividual clay, silt, or sand particles, particle assemblage as unitsof particle organization having definable physical boundaries and porespaces as fluid and/or gas filled voids within the soil fabric. SeeMitchell, J. K. (2005), “Fundamentals of soil behaviour”, 3rd Edition,John Wiley and Sons, Inc., New York, incorporated herein by reference inits entirety. Mitchell divided the fabric of a soil into three levels ofscale as microfabric, minifabric, and macrofabric. Microfabric isdefined as regular aggregations of particles and the very small poresbetween them; typical fabric units are up to a few tens of micrometersacross. The minifabric consists of the aggregations of the microfabricand the interassemblage pores between them; minifabric being a fewhundred micrometers in size. Finally, macrofabric may contain cracks,root holes, laminations, and the like that correspond to thetransassemblage pores. Abduljauwad and Al-Sulaimani carried out detailedresearch on the swelling potential of the clay soils in Qatif area ofSaudi Arabia. See Abduljauwad. S. N. and Al-Sulaimani, G. J. (1993),“Determination of Swell potential of Al-Qatif Clay”, GeotechnicalTesting Journal, ASCE, December 1993, pp. 469-484, incorporated hereinby reference in its entirety. As a result of these studies, they foundsubstantial differences in the swelling potential assessed from thelaboratory conventional Oedometer tests, laboratory tests on large scaleblock samples, and field tests on the subsurface strata (Table 3). Theyattributed these differences to the contribution of several macro tonano level structural features that might have been masked in the smallscale laboratory tests. Moreover, El Sohby and Rabba also showed thatswell percentage and pressure does not have a linear relationship withthe various percentages of sand and silt content (FIGS. 1A and 1B). SeeEl Sohby, M. A. and Rabba, E. A. (1981), “Some Factors affecting theswelling of clayey soils”, Geotechnical Engineering, Vol 12, page 19-39,incorporated herein by reference in its entirety.

TABLE 3 Comparison of swelling potential based on the results from thelaboratory and field tests (Abduljauwad and Al-Sulaimani, 1993).Percentage Swelling Heave, Method of Swell, % Pressure, kPa mm OedometerImproved simple oedometer 36 3100  63.9 Constant volume — 800 47.5Reverse curve 8.8 2000  58.6 Suction — — 36.8 Triaxial 14.3 420 39.6Simulation swelling test 15.0 — 37.4 Field 15.4 180 38.4

Based on the premise by Mitchell and the conclusions of Abduljauwad etal. and El Sohby and Rabba, it seems that in addition to macro to nanolevel behavior, macro to nano level features should also be consideredin the constitutive modeling of expansive clays. See Abduljauwad, S. N.,Al-Sulaimani, G. J., Basunbul, I. A., and Al-Buraim, I. (1998),“Laboratory and field studies of response of structures to heave ofexpansive clay”, Geotechnique, 48(1): 103-121, incorporated herein byreference in its entirety. Gens and Alonso presented a mathematicalmodel for the expansive clays. See Gens, A. and Alonso, E. E. (1992), “Aframework for the behavior of unsaturated expansive clays”, CanadianGeotechnical Journal 29, 1013-1032 (1992), incorporated herein byreference in its entirety. Lumped fabric consisting of micro and nanolevel pores and idealization of a single mineral fabric attained undercontrolled compaction conditions by Gens and Alonso and their followersmight not have led to the formulation of a complete representativebehavior model.

Nano or molecular level processes may play a role in understanding thevolume change behavior of expansive clays. Some studies have beenconducted to simulate the swelling and/or water absorption behavior ofthe single or isolated expansive clay minerals, but modelling of thereal/natural expansive soil fabric and its interaction with pore fluidsat molecular level is still lacking. Moreover, no efforts have beendirected to couple the macro and micro scale material behavior based onthe findings of these molecular simulations. As molecular level modelingstudies could lead to the real insights into soil behavior, it wouldresult in the validation and/or modifications of several macroscopic(continuum) constitutive behaviors. Recent advances in numericalcomputational methods, high performance hardware, molecular modelingsoftware, and experimental techniques could be used to provide the realinsight into the real behavior at the molecular level.

Attempts to predict the expansive or swell potential of expansive clayminerals or expansive clayey soils comprising expansive clay mineralshave not been able to provide a comprehensive understanding for thevarious possible variations in the fabric and structure of the naturaland compacted expansive clayey soils. Since the emergence of theunsaturated geotechnical engineering, performance of numerical modelingof the realistic volume change behavior of the expansive clays is achallenge for the geotechnical engineers. Consequently, several effortshave been made to develop constitutive models for the behavior of theexpansive soils by performing parametric study mostly at the macrobehavior level and to quite lesser extent at molecular level. All thedeveloped constitutive models do not comprehensibly incorporate thecoupling of the behavior at the macro, micro, and nano levels. Moreover,most of the developed constitutive models pertain to the standardexpansive clay minerals compacted under controlled conditions; modelscovering the natural and real soil fabric do not exist.

Lack of proper understanding and knowledge of the molecular and nanolevel interactions of the clay minerals with the pore fluids and theother non-swelling constituents have limited the development of specificconstitutive models encompassing the accurate behavior under severalpossible combinations of clay, fluid and other non-swelling particles.This behavior becomes further complex for the swelling clays when theinteraction between clay, fluid, and the non-swelling clay particlesbecome predominant.

The present disclosure covers the general comprehension of the fabricand structure of the swelling clays, swelling mechanism, and thecorresponding level of efforts in the constitutive and molecular levelmodeling of expansive clayey soils. All these pertinent issues relatedto expansive clays are discussed in detail herein.

The excessive volume change tendency of expansive clays is mainlyattributed to the presence of expansive clay minerals in the soilfabric. These expansive clay minerals have got high affinity to thewater and dissolved ions due to the net unbalanced electrical chargespresent on their surfaces. Volume change of the clay structure occursonce these expansive minerals absorb water and move from one partiallysaturated state to another. The volume change behavior is invariablycontrolled by many factors including type of clay minerals, currentdegree of saturation, past wetting-drying cycles, fabric and structurecreated during the compaction/natural deposition, presence ofnon-expansive minerals, their sizes, percentages and distribution in thematrix. A comprehensive constitutive model should encompass all thesefactors and their relative contribution to thephysico-chemical-mechanical interactions at various scale levels. Inorder to integrate all these factors in a constitutive model,understanding the behavior of the fabric at micro and nano level and itsassociation with the macro behavior is required.

Most of the expansive clay minerals belong to the Smectite group andtheir typical expandable structure consisting of alternate silicate andalumina sheets is shown in FIG. 2 (Mitchell). Each clay particle couldbe conceptualized as a flake/sheet like structure having dimensions ofan order of nanometer with a length or width to thickness ratio of about2000:1. See Sharma, R. S. (1998), “Mechanical Behavior of UnsaturatedHighly Expansive Clays”, PhD Thesis, Oxford University, UK, incorporatedherein by reference in its entirety. The clay particles are alsoreferred to as particles, lamellae or micelles at these finest levels.See Quirk. J. P. and Murray. R. S. (1991), “Towards a model for soilstructural behavior”, Australian Journal of Soil Research 29, 829-867;Oades, J. M. and Waters, A. G., (1991), “Aggregate hierarchy in soils”,Australian Journal of Soil Research, 29, 815-828, each incorporatedherein by reference in their entirety. Isomorphous substitution, brokenedges, and eccentric positive and negative charge centers result in netunbalanced charges on these particles. As a result of these unbalancedcharges, these clay particles or sheets combine to form platelets ofeach about ten sheets (100:1) (Oades and Waters). These have also beencalled grains, crystals or quasi-crystals (Quirk and Murray). Variousbonding forces ranging from hydrogen bonds in kaolinite to van der Waalsand cation bonding in montmorillonite exist in the individual clayparticles or sheets. The group of platelets are present asmicro-aggregates (Oades and Waters) and clusters at the microscopiclevel and peds, macro-aggregates (Oades and Waters) or prisms at macrolevel. See Thomasson, A. J. (1978), “Towards an objective classificationof soil structure”, Journal of Soil Science 29, 38-46; Cabidoche, Y. M.and Ruy, S. (2001), “Field shrinkage curves of a swelling clay soil:analysis of multiple structural swelling and shrinkage phases in theprisms of a vertisol”, Australian Journal of Soil Research 39, 143-160,each incorporated herein by reference in their entirety.

Lambe provided a conceptual picture of the clay fabric, although hiswork was mainly related to the compacted clays only. See Lambe, T. W.(1958), “The structure of compacted clay”, Journal of Soil Mechanics andFoundations Division, ASCE, Vol. 84 (SM2), 1654, incorporated herein byreference in its entirety. He defined the bimodal fabric on dry side andmassive and unimodal fabric on wet side of the optimum with themicrovoids in between platelets and macrovoids in group of platelets. Inhis models, he identified three levels of fabric corresponding to threelevels of void fluid filled spaces, intra-platelet spaces betweenindividual unit layers, small voids (microvoids) between individual clayplatelets between larger flocs of packets of soils, and macrovoidsbetween larger flocs and packets.

Gens and Alonso, considered as pioneers in formulating the firstconstitutive model framework for the expansive soils, envisaged anexpansive clay fabric (FIGS. 3A, 3B and 3C). They conceptualized thestructural arrangement consisting of three basic microfabric features:elementary particle arrangements or quasi-crystals, particleassemblages, and pore spaces. Gens and Alonso described the particleassemblages formed by arrays of elementary particle arrangements asmatrices. In their model, pore spaces in the matrices are made up ofintramatrix pores existing between elementary particle arrangements.Elementary particle arrangements join together to make aggregatesresulting in a three-dimensional structure of a granular type. Bothinter and intra-aggregate pore spaces exist in the aggregated structure.A further level of void space also exists in the intraelement poresseparating the clay platelets in the elementary particle arrangements.They related both the expansive and collapse type of phenomena to theseforms of fabric. Clay structure conceptualized by Gens and Alonso wasfurther supported by SEM micrographs of clay samples at optimum and dryand wet sides of optimum by Delage and Graham. See Delage, P. andGraham, J. (1996), “Mechanical behavior of unsaturated soils:understanding the behavior of unsaturated soils requires reliableconceptual models”, In: Alonso EE and Delage P. (eds), Proceedings of1st International conference on Unsaturated Soils, Paris, vol. 3,Balkema Presses des Ponts et Chaussees pp. 1223-1256, incorporatedherein by reference in its entirety. Conceptual clay structure in FIGS.3A, 3B and 3C, respectively, represents the fabric on wet and dry sideof optimum. However, one of major limitation in Gens and Alonso model isthe consideration of the two micro level voids as one. This leads to thepresence of two global levels only (intraplatelet spaces and microvoidsbetween platelets) and contradicting the fact that microvoids andintervoid space between platelets may also be present in an unsaturatedstate. Therefore, their model may only be considered applicable toheavily compacted clays such as ones being used for the nuclear andother types of waste containment. Likos and Lu were the first toconsider a more realistic fabric consisting of inter-aggregate,intra-aggregate (or inter-particle) and interlayer space levels. SeeLikos, W. J. and Lu, N. (2006), “Pore scale analysis of bulk volumechange from crystalline swelling in N+- and Ca2+-smectite”, Clays andClay Minerals, Vol. 54, No. 4, pp. 516-529, incorporated herein byreference in its entirety. Their model is shown in FIGS. 4A, 4B and 4C.

The clay fabric was also further elaborated by Sharma, defining themicro and macro structure as assemblage of particles with three levelsof voids as micro, macro and intra platelet voids. His conceptual modelis shown schematically in FIGS. 5A, 5B and 5C. Sanches et al. alsoadopted the model of Gens and Alonso considering the two general levelsof structures (FIG. 6) and the assumption that microstructure is beingconsidered as saturated at all the field conditions. See Sanchez, M.,Gens, A., Guimaras, L. N. and Olivella, S. (2005), “A double structuregeneralized plasticity model for expansive materials”, InternationalJournal for Numerical and Analytical Methods in Geomechanics, 2005,29:751-787, incorporated herein by reference in its entirety. Pinyol etal. studied and modeled the weathering of the soft clayey rocks and alsoconsidered a model similar to the Gens and Alonso with the addition ofcementation at the platelet contacts. See Pinyol, N., Vaunat, J. andAlonso, E. E. (2007), “A constitutive model for soft clayey rocks thatincludes weathering effects”, Geotechnique 57, No. 2, 137-151,incorporated herein by reference in its entirety. They also modeled thedegradation of the cementation upon cyclic loading and weatheringconditions. The conceptual model prepared by them for the cyclic loadsimulation is shown in FIG. 7. This model could be considered apromising attempt to incorporate natural soil behavior but may beapplicable to the homogenous type of clay rocks only and not to thesoils consisting of multiple minerals. Moreover, Pinyol et al. did notconsider the effects of presence of fissures and cracks present in thenatural clay fabric. These fissures and cracks should be consideredinherent part of the natural deposits and contribute significantlytowards the digenesis and weathering processes.

Fityus and Buzzi discussed and reviewed the effects of the claymicrofabric on the volume change of the macrofabric in the existingmodels. See Fityus, S. and Buzzi, O (2008), “The place of expansiveclays in the framework of unsaturated soil mechanics”, Applied. ClayScience, Vol. 43, Issue 2, page 150-155, incorporated herein byreference in its entirety. They conceptualized clay structure as a groupof aggregates and clusters into single structural element group calledpeds. A ped is a naturally occurring, structured soil element within aripened (Pons and Van der Molen) heavy clay soil; that is bounded bydiscontinuities (typically cracks) that separate it from the adjacentelements of similar form. See Pons, L. J. and Van der Molen, W. H.(1977), “Soil genesis under dewatering regimes during 1000 years ofpolder development”, Soil Science 116, 228-235, incorporated herein byreference in its entirety. The ped could therefore be considered asbasic unit of natural heavy clay soil at the macro scale. Particle sizeof montmorillonite particle size being in the order of 50 to 1600 nm(Robertson et al.), it becomes difficult to characterize the structureand the pore spaces even using the most advanced and sophisticatedEnvironmental Scanning Electron Microscope (ESEM) and X-ray ComputedTomography (CT) scanning or mercury porosimetry techniques (Fityus andBuzzi). See Robertson, H. E., Weir, A. H. and Woods, R. D. (1968),“Morphology of particles in size fractionated Na montmorillonite”, Claysand Clay Minerals 16, 239-247, incorporated herein by reference in itsentirety. Both naturally occurring soils and soils created from theconsolidation of slurries have a very small pore size of an order of3-10 nm and air entry value of 80-100 MPa as reported by Alymore andQuirk, Oades and Waters, Villar, and Meunier. See Alymore, L. A. G. andQuirk, J. P. (1962), “The structural status of clay systems”, In:Swineford, A. (Ed.), Proceedings of the 9th National Conference on Claysand Clay Minerals, Lafayette, Ind., pp. 104-130; Villar, M. V. (2000),“Thermo-hydro-mechanical characterization of a bentonite from CabodeGata”, PhD Thesis, Universidad Complutense, Madrid, Spain; Meunier, A.(2006) “Why are clays minerals small”, Clay Minerals 41, 551-566, eachincorporated herein by reference in their entirety. Based on this fact,saturation of the peds pass through drying and shrinkage cycles withoutany water loss and complete saturation is ensured at all the fieldsuction values. However, Terzaghi's saturation and effective stressconcepts could not be considered applicable to the saturated peds (Lambeand Whitman; Sridharan and Venkatappa; Heuckel. See Lambe, T. W.,Whitman, R. V. (1959), “The role of effective stress in the behavior ofexpansive soils”, First Annual Soil Mechanics Conference, ColoradoSchool of Mines, pp. 33-65; Sridharan, A., Venkatappa R. G. (1973),“Mechanisms controlling volume change of saturated clays and the role ofthe effective stress concept”, Geotechnique 23, 359-382; Hueckel, T. A.(1992), “Water-mineral interaction in hygromechanics of clays exposed toenvironmental loads: a mixture-theory approach”, Workshop on StressPartitioning in Engineered Clay Barriers, May 29-31, 1991, DukeUniversity, Durham, N.C. 1071-1086, each incorporated herein byreference in their entirety. The structure envisioned as saturated soilpeds separated by air-filled macroscopic desiccation cracks (FIG. 8)confirms that it cannot be modeled either as continuum or as unsaturatedsoils due to non-existence of surface films and water bridges.

Likos and Wayllace studied the porosity evolution of free and confinedbentonite during the phase of the interlayer hydration. See Likos, W.J., Wayllace, A. (2010), “Porosity Evolution of Free and ConfinedBentonites During Interlayer Hydration” Clays and Clay Minerals, Vol. 58(3), pp. 399-414, incorporated herein by reference in its entirety. Theycame up with a bimodal porosity model developed for Wyoming bentoniteusing SEM image of the compacted bentonite. The schematic sketch of themodel at several levels is shown in FIGS. 9A, 9B, 9C, 9D, and 9E.Hueckel, while presenting his mixture theory approach for water-mineralinteraction in clays under environmental loads provided in a schematicsketch various forms of water in high density clayey soil. His conceptof various forms of water and the corresponding pores in a natural soildeposit are shown in FIG. 10.

In addition to the fabric visualization of the expansive clayey soils,another important input required in any molecular levelmodeling/simulation is the size of the fundamental smallest clay mineralcrystallites. Several researchers have come up with a fundamental sizeranging from as small as 100 Å (Longuet-Escard et al.) to much greaterthan 1000 Å. See Longuet-Escard, J., Mering, J., and Brindley, G.(1960), “Analysis of hk bands of montmorillonite”, C. R. Acad, Sci,Paris 251, 106-108, incorporated herein by reference in its entirety.Most probable reason for such wide range of clay mineral crystallite isthe method used for the determination of the size. It has been observedthat at most of the times, the imaging or mapping methods involve use ofdry specimens. In dry form, the crystallites most probably get fused atthe edges and ends and grow into larger crystallites. Moreover,flocculated fabric may also be responsible for such discrepancy.Therefore, the techniques involving the wet specimens such as ESEM andin the dispersed fabric form could provide the real fundamentalcrystallite size for clay minerals.

The above discussions on the fabric of clays being conceptualized in theexisting constitutive models reveal that there are several underlyingsimplified assumptions that obscure the real behavioral contributionfrom several levels. This fact is particularly true for themolecular/nano level contributions to macro level behavior. All theexisting models ignore the molecular level considerations in theirassumed clay fabric and hence its fundamental role in the overallbehavior of expansive clays.

Highly charged clay particles/platelets make bonds with water and thedissolved ions to satisfy their charges and consequently an expansion oftheir structures occurs. These expanded structures have a tendency tocollapse compress/shrink upon loss of water. Clay particle-waterinteraction theories date back to early 20th century when Guoy andChapman came up with their diffuse double layer (DDL) theory. See Gouy,G. (1910), “Sur la constitution de la charge electrique a la surfaced'un electrolyte”, Annales de Physique (Paris), Serie 4, 9, 457-468;Chapman, D. I. (1913), “A contribution to the theory ofelectrocapillarity”, Philosophical magazine, Vol. 25 (6), 475-481, eachincorporated herein by reference in their entirety. This theory waslater on further refined by Stern. See Stern S. (1924), “Modification inDiffuse Double Layer Theory”, Z. Elektrochem., Vol. 30, p. 508,incorporated herein by reference in its entirety. In order to satisfycharges, DDL develops for individual clay units and platelets and isschematically shown in FIG. 11. DDL can successively model the effectsof cation valence, dielectric constant, electrolyte concentration, andtemperature. However, there are certain limitations associated with DDLsuch as cations are being considered as point charges, DDL may notdevelop in highly compacted soils and there is less likelihood ofpresence of parallel clay particles in real clay fabric. Recently,Wayllace developed a general understanding of the structure of theswelling clay minerals, short and long-term water adsorption mechanisms,and influences of particle and pore fabric on swelling behavior usingthe porosity evolution model developed by Likos and Lu; the model isconceptually shown in FIG. 12. See Wayllace, A. (2008), “Volume changeand swelling pressure of expansive clay in the Crystalline swellingregime”, PhD Thesis, University of Missouri, US, incorporated herein byreference in its entirety.

Wayllace divided the water adsorption phenomenon of the clay mineralsinto three micro-scale mechanisms as hydration, capillarity, andosmosis. Hydration and osmosis play a central role in two main clayswelling processes i.e. crystalline and osmotic swelling (Marshall; VanOlphen; madsen and Muller-Vonmoos). See Marshall, C. E. (1949) “TheColloid Chemistry of the Silicate Minerals”, New York: Academic Press,P. 54; Van Olphen, H. (1977), “An introduction to clay colloidchemistry”, 2nd ed. New York: John Wiley and Sons; Madsen, F. T. andMuller-Vorunoos, M. (1989), “The swelling behavior of clays”, AppliedClay Science4:143-56, each incorporated herein by reference in theirentirety. Capillary mechanism is responsible only for the provision ofthe water for other major and short-ranged water adsorption mechanisms(Snethen et al.; Miller). See Snethen, D. R., Johnson, L. D. andPatrick, D. M. (1977), “An Investigation of the Natural MicroscaleMechanisms That Cause Volume Change in Expansive Clays” Federal HighwayAdministration Report No. FHWA-RD-77-75; Miller, D. J. (1996) “Osmoticsuction as a valid stress state variable in unsaturated soils” Ph.D.dissertation, Colorado State University, Fort Collins, Colo., eachincorporated herein by reference in their entirety. Wayllace emphasizedthe importance of the crystalline or type-I swelling as the keymechanism leading to a better understanding of the swelling behavior.Crystalline swelling is a process whereby expandable 2:1 phyllosilicatessequentially intercalate one, two, three or four discrete layers of H₂Omolecules between the mineral interlayer (Norrish) shown schematicallyin FIG. 13. See Norrish, K. (1954), “The Swelling of Montmorillonite”,Transaction Faraday Society 18: pp. 120-134, incorporated herein byreference in its entirety. Type-II swelling mechanism involves thehydration of the cations dissolved in the water layers. For example, VanOlphen calculated that for Ca-montmorillonite, the pressure associatedwith removing the water from the fourth, third, second, and firsthydration states were 20,000 kPa, 125,000 kPa, 250,000 kPa, and 600,000kPa, respectively. See Van Olphen, H. (1963), “Compaction of ClaySediments in the Range of Molecular Particle Distances”, Clays and ClayMinerals, Vol. 11, pp. 178-187, incorporated herein by reference in itsentirety.

Osmotic theory has also been used to explain the swellingcharacteristics of the clay particles (Bolt). See Bolt, G. H. (1956),“Physico-chemical Analysis of the Compressibility of Pure Clays”,Geotechnique, Vol. 6, No. 2, pp. 86-93, incorporated herein by referencein its entirety. An equilibrium analysis is carried out between the unitlayers, clay platelets, and water by balancing the external and internalforces in order to achieve the maximum number of layers in a platelet.In order to maintain equilibrium, water flows from low concentration(bulk water) to higher concentration of ions (DDL water) and increasesthe pressure in the DDL. This high pressure in turn causes the tendencyto have a reverse flow till a balance is reached.

Few efforts have also been made at nano level to model the swellingmechanism of the swelling clays. The results of these studies are insome cases in contradiction of the general understanding of the swellingclays. This emphasizes the need for nano level modelling andconsequently refinement and augmentation of the existing micro and macroscale models.

Swell potential modeling of expansive clays have been carried out byseveral researchers with an objective of formulating the representativeconstitutive models. In this regards, efforts have been made at macro,micro, and nano/molecular levels to constitute behavior models for theexpansive clays. Most of the constitutive modeling studies have beencarried out at macro/micro levels and the simulations have beenperformed at nano molecular level.

Constitutive model of expansive clays could be considered as a specialcase of the general constitutive models for the unsaturated soils. Inthe realm of unsaturated soils, Matyas and Radhakrishna could beconsidered as the pioneers to create the concept of state (constitutive)surfaces relating the void ratio and degree of saturation with the stateparameters net stress, p and suction, s. See Matyas, E. I. andRadhakrishna, H. S. (1968), “Volume change characteristics of partiallysaturated soils”, Geotechnique, Vol. 18 (4), 432-448, incorporatedherein by reference in its entirety. These surfaces are characterized byone of the very basic observation of the wetting induced swelling at lowmean net stress while wetting induced collapse/compression at high meannet stress. The idea of state surfaces was, later on, extended anddeveloped by Fredlund and Morgenstern and Fredlund and was called StateSurface Approach (SSA). See Fredlund, D. G. and Morgenstern, N. R.(1977), “Stress state variables for unsaturated soils”, Journal ofGeotechnical Engineering Division, ASCE, Vol. 103(GT5), 447-466;Fredlund, D. G. (1979), “Appropriate concepts and technology forunsaturated soils”, Canadian Geotechnical Journal, Vol. 16, 121-139,each incorporated herein by reference in their entirety. The equationssuggested by the authors represent the planar surfaces and are limitedby the fact that these do not account for the wetting induced collapseand swelling. Moreover these are valid only for monotonic loading andnot for wetting and drying cycles. In addition, as stated above, nodistinction can be made between elastic and plastic strains as these areonly representative of the elastic zones. However, Fredlund (1979)suggested that these relations could be representative of theelasto-plastic strains if constants are functions of stress state. Lateron, Lloret and Alonson proposed state surfaces relating void ratio anddegree of saturation. See Lloret, A. and Alonso, E. E. (1985), “Statesurfaces for partially saturated soils”, Proc 11th Conference on SoilMechanics and Foundation Engineering, Sand Francisco, Vol. 2, 557-562,incorporated herein by reference in its entirety. Although theserelations represent surfaces that can simulate the wetting inducedcompression and swelling behavior but these were again valid only over alimited stress interval.

Alonso et al. (1987) were the first ones to present an integratedvolumetric and shear strength elasto-plastic framework of theunsaturated soils. See Alonso, E. E., Gens, A. and Hight, D. W. (1987),“Special Problem Soils, General Report”, Proceedings 9th EuropeanConference on Soil Mechanics, Dublin, Vol. 3, 1087-1146, incorporatedherein by reference in its entirety. The qualitative framework wasfurther developed into its mathematical form by Alonso et al. (1990) intheir landmark paper and was named Barcelona Basic Model (BBM). SeeAlonso, E. E., Gens, A. and Josa, A. (1990), “A constitutive model forpartially saturated soils”, Geotechnique, Vol. 40(3), 405-430,incorporated herein by reference in its entirety. It would be quitecorrect to state that all the recent models for unsaturated expansiveand non-expansive soils are based on the same core of the BBM. Alonso etal. (1990) provided a complete mathematical formulation of the criticalstate based model for non-expansive or slightly expansive unsaturatedsoils. Four state variables i.e., mean net stress, suction, deviatorstress, and the specific volume were used to formulate the model. Theprojection of the yield surface on p-s space (isotropic stress space) isa curved line known as Load-Collapse (LC) curve and shown in FIGS. 14A,14B, 14C and 15. Plastic compression at high stress level upon wettingis modeled in a similar way as the plastic compression after crossingthe yield point and change of specific volume upon plastic yielding.Volumetric decrease as a result of the increase in suction is delimitedby the yield surface or limiting line of Suction Increase (SI) shown inFigures ISA, 15B, 15C, and 15D. Both SI and LC together mark the areacharacterized as elastic zone. They used the modified cam clay model asthe interface with the saturated counterpart. Therefore, yield surfaceis an ellipse in anisotropic states in q:p plane at all suctions (FIG.16). Although non-linearity of the shear strength is well establishedbut for the sake of the simplicity for the initial model, it has beentaken as linear. Their proposed shear strength equation collapses to theone proposed by Fredlund (1979) when c′=0. They proposed non-associatedflow rule model to match well with the Ko conditions of saturated sand.Ten soil constants are required for the development of the model whilecurrent soil state is defined as p, q, s and v or p, q, s and p(0). Themodel developed by Alonso et al. (1990) is volumetric in nature only andno consideration of mechanical behavior is taken in the model.Simplifying assumptions adopted in the model are the use of straightlines for the e-ln p relationships (implying a continuous increase ofthe collapse strains upon wetting) and the linear increase of apparentcohesion with suction. Moreover, no hydraulic hysteresis has beenincorporated in the model. In spite of its basic nature, BBM was quiteable to define several typical behaviors of unsaturated soils such asthe variation of wetting-induced swelling or collapse strains dependingon the magnitude of applied stresses, the reversal of volumetric strainsobserved during wetting-induced collapse, the increase of shear strengthwith the increase in suction, stress path independency associated withwetting paths and the opposite when the stress path involves drying orthe apparent increase of pre-consolidation stress with suction. BBMbecame a basis for its specific and advanced model for the expansivesoils, BExM.

As BBM was developed for the non-expansive or slightly expansive soils,Gens and Alonso provided a breakthrough in the provision of a conceptualmodel encompassing the behavior model for expansive clays. The model wasbased on the behavior of an extension of the BBM. This model covers thelimitation of the BBM to model the large strain behavior of expansivesoils and hence introduced a microstructure model to be coupled with themacrostructure model of Alonso et al. (1990). In their coupled models,soil structure has been divided into two distinct levels i.e. micro andmacro. Microstructure consists of quasi-crystals, particles assemblages,and pore spaces, while assemblages together formulate matrix in whichlarge sized sand and silt particles are embedded. The extended modelincorporates a microfabric of clay particles and aggregations embeddedinto an overall macrofabric of silt and sand size particles. Theelementary particles group together to form aggregations and resultingin granular type of structure. The pores sizes in the formulatedstructure are present both as intra and inter aggregations. Theyconsidered microfabric to be only affected by the local stresses andhence effective stress principles may be applicable and volume change inmicrofabric to be reversible and unaffected by strain in themacrofabric. This assumption leads to the fact that if sum of net stressand suction (p+s) remains constant, then no change in overall volumewould occur and the stress state moves on a line known as neutral line(FIG. 17). The microfabric in their model is essentially consideredsaturated even if the overall saturation of the soil fabric is notachieved. Although, micro structural level behavior remains generallyindependent of the macrostructure behavior and is basically controlledby the physicochemical processes causing volume variations, there is anobvious interaction and this has been covered in the extended model bycoupling of the micro and macro structure (FIGS. 18A and 18B).Therefore, the extended model for expansive clays should consist ofthree elements as soil behavior at macroscale, behavior at microscale,and the coupling between the two levels. One of the major limitations ofthe Gens and Alonso model was the assumption regarding the permanentsaturation of the microfabric as that does not seem to be realistic asmicrovoids/inter platelet voids may remain unsaturated as well. Thepermanent saturation of the microfabric may be considered valid only forthe intraplatelet fabric only. Moreover, this model was mainlyconceptual in nature and no detailed mathematical formulation wasprovided till a complete mathematical model by Alonso et al. (1999),named as Barcelona Expansive Model (BExM). See Alonso, E. E., Vaunat,J., Gens, A. (1999), “Modeling the mechanical behavior of expansiveClays”, Eng Geol 1999; 54:173-83, incorporated herein by reference inits entirety.

Up to this stage, it is clear that modeling of expansive clays requireconsideration of three basic elements: microstructure model,macrostructure model and the interaction in the form of couplingfunctions. From Gens and Alonso model onwards, both the micro and macrolevel models of the unsaturated soils were mostly handled independentlyby several researchers. However, most of the researchers worked towardsthe development and improvement of the unsaturated soil model fornon-expansive soils, while only few accomplished some improvements andvariations in the expansive clays model.

Alonso et al. (1999) had a landmark contribution in expansive claysmodel by developing a mathematical model for expansive clays based onthe concepts developed in the models of Alonso et al. (1990) and Gensand Alonso. Two additional yield surfaces, one for plastic yieldingcaused by suction increase (SI) and the other by suction decease (SD),were introduced (FIGS. 19 and 20). These surfaces are parallel to theneutral loading line in the space of net mean stress versus suction, andare coupled to the LC surface through two experimentally determinedfunctions. The model by Alonso et al. (1999) is able to predict theirreversible expansion caused by wetting at low stresses and shrinkageat high stresses. In this model, macro-structural plastic volumetricchange causes a corresponding change in the location of the LC. When themacro-structure becomes looser, the macro-structural yield surfaceshrinks. When the structure becomes denser, the elastic domain increasesand LC expands. A coupling therefore exists between yield surfaces LC,SI and SD (FIGS. 19 and 20). However, irreversible change of degree ofsaturation during cyclic wetting and drying was not considered in themodel of Gens and Alonso or of Alonso et al. (1999) and this hasremained one the major limitation of these models even to the present.

After Alonso et al. (1999) BExM, major contribution towards thedevelopment of the expansive clay models was done by Sanchez et al. whoformulated an expansive clays model considering concepts of classicaland generalized plasticity theories and is shown in FIGS. 21A and 21B.They developed generalized stress-strain rate equations from the conceptof a framework of multi-dissipative materials. This framework provides aconsistent and formal approach when there are several sources of energydissipation and is well suited for the modeling of generalized stressreversals. They used a generalized plasticity model for the materialsthat show irrecoverable deformations upon reloading and also to includethe behavior of soils under cyclic loading when they exhibitirreversible deformation in loading, unloading, and reloading. They weresuccessful in modeling the typical aspects of the behavior observed inexpansive soils under generalized stress paths including suction andstress changes. The authors attributed significant advantages in usinggeneralized plasticity theory to model the plastic mechanism related tothe interaction between two levels of pores structures.

Sanchez et al. formulated the model in the space of stresses, suctionand temperature; and implemented the double structure approach in afinite element program CODE BRIGHT. The mechanical law of this model isable to model the macropore invasion induced by microstructureexpansion, when conditions of high confinement prevail consideringnegative values of the function fs for high values of p=po (FIGS. 21 and22). In FIG. 22, point at which both interaction curves meet, indicatedas E; is the equilibrium point. This point represents the state of thematerial for which no cumulative deformations are observed after cyclesof suction changes.

Next major contribution in the modeling of expansive clays could beconsidered by Pinyol et al. who investigated the dual nature ofClaystone by developing independent constitutive models for theirrock-like and clay-like behavior. Claystone acts like a Rock whenpresent in the unweathered state while it behaves as Soil in itsweathered state. The authors attributed this dual behavior to thepresence of basic clay matrix and the quasi-brittle cementation at themicrostructure level. They considered the matrix behavior by theelasto-plastic double structure model proposed by Gens and Alonso andAlonso et al. (1999), while cementation/bonding was modeled using thedamage mechanics based model. They demonstrated the effectiveness of thedeveloped integrated models through the data generated throughexperimentation. Models by Pinyol et al. could also be considered asubstantial contribution in modeling the natural homogenous types ofclay.

The challenge with BExM is that the micro parameters and the functioncoupling the micro and macro structural strains are difficult todetermine experimentally. Moreover, BExM is mainly concentrating on thestress-strain and strength behavior without considering the waterretention behavior of the expansive soils. In this respect, severalmodels have been developed for unsaturated soils but no such effort hasbeen made for expansive soils. Sun and Sun developed an elasto-plasticconstitutive model for predicting the hydraulic and mechanical behaviorof unsaturated expansive soils based on an existing hydro-mechanicalmodel for unsaturated non-expansive soils. See Sun. W. and Sun, D.(2011), “Coupled modeling of hydro-mechanical behavior of unsaturatedcompacted expansive soils”, International Journal of Numerical andAnalytical Methods in Geomechanics, Vol. 36, Issue 8, page 1002-1022,incorporated herein by reference in its entirety. They basicallydeveloped the first macroscopic elastoplastic model for unsaturatedexpansive soils and also introduced the concept of equivalent void ratiocurve to distinguish between the yield curve and plastic potentialcurve. Basis is the experimental data and the model developed forunsaturated non-expansive soils. This model incorporates the coupledhydro-mechanical effect of degree of saturation on the mechanicalbehavior and void ratio on the water-retention behavior. Sun and Sunargued that compression index of swelling clays have been found to beincreasing with increase in suction while it decreases with increase insuction for unsaturated non-expansive soils. This is a fundamentaldifference among the compressibility behavior of the unsaturatednon-expansive and expansive soils. Their hydro-mechanically coupledelastoplastic model can predict the hydraulic and mechanical behavior ofunsaturated expansive soils. While developing that model, they assumedthat pore air and pore-water are continuous throughout the soil voidswhich are basically true for some regime of water content (degree ofsaturation) only. Besides being a macroscopic model, this is in fact amajor limitation of the model.

Guimaraes et al. may be considered as the pioneer in the formulation ofa chemo-mechanical model for the expansive clays with due considerationof the contribution from cation content, osmotic suction, and the cationexchange. See Guimares, L. D., Gens, A., Sanchez, M., and Olivella, S.(2013), “A chemo-mechanical constitutive model accounting for cationexchange in expansive clays”, Geotechnique 63, No. 3, 221-234,incorporated herein by reference in its entirety. Their model is acontribution to the microstructure model in the double-structureapproach used by Sanchez et al. Their main assumption regarding theelastic or reversibility of the microstructure behavior remains thesame. They introduced additional parameters for the microstructure to beincorporated into the constitutive model. Although, the model is quitecapable of predicting the behavior of saturated and unsaturatedbehavior, but most of the basis is through the indirect inferences frommacro level studies and no input from molecular level has beenincorporated.

Expansive clay minerals are nano-materials and nano-mechanics conceptscan be used to improve fundamental understanding of the behavior andpredict the volumetric changes under the desired boundary and stressconditions. By obtaining molecular-scale material properties, themacro-scale material behavior can be obtained, with limited inputparameters and with great accuracy and details.

For the purpose of molecular nano level simulations, most commonlyadopted technique is the Molecular Dynamics (MD). MD is a computationalmethod which calculates the time dependent behavior of a molecularsystem. MD is based on Newton's second law of motion and provides atrajectory which specifies the variation of position and velocity ofindividual atoms in a molecular system with time. In this technique,Individual atoms are characterized by balls with bonds represented assprings. A variety of springs are introduced that capture stretching,angular rotation, and torsion non-bonded interactions are modeled as vander Waals and electrostatic. In MD, individual atoms would berepresented by the balls and the connecting major bonds as springs,while non-bonded interactions among the molecules would be representedby the van der Waal's and electrostatics. The potential energy of thesystem is then calculated using a force-field and is used to calculatethe trajectory of the atoms in a molecular system. Force-field (Brookset al.) is generally given by (see Brooks, B. R., Bruccoleri, R. E.,Olafson, B. D., States, D. J., Swaminathan, S., Karplus, M. (1983),“CHARMM: A program for macromolecular energy, minmimization, anddynamics calculations”. J. Comp. Chem. 4, 187-217, incorporated hereinby reference in its entirety):

$\begin{matrix}{E_{Total} = {E_{coul} + E_{VDW} + E_{{Bond}\;{Stretch}} + E_{AngleBend} + E_{Torsion}}} & \text{2-1} \\{where} & \; \\{E_{Coul} = {\frac{e^{2}}{4\;\pi\; ɛ_{0}}{\sum\limits_{i \neq j}\frac{q_{i}q_{j}}{r_{ij}}}}} & \; \\{E_{VDW} = {\sum\limits_{i \neq j}{D_{o}\left\lbrack {\left\lbrack \frac{Ro}{r_{ij}} \right\rbrack^{12} - {2\left\lbrack \frac{R_{o}}{r_{ij}} \right\rbrack}^{6}} \right\rbrack}}} & \; \\{E_{BondStretch} = {k_{1}\left( {r - r_{0}} \right)}^{2}} & \;\end{matrix}$

Skipper et al. performed the swelling simulation of various clayminerals using Monte Carlo (MC) simulation technique. See Skipper, N.T., Sposito, G., and Chang, F. R. (1995a), “Monte Carlo simulations ofinterlayer molecular structure in swelling clay minerals 1.Methodology”, Clays and Clay Minerals, Vol. 43, No. 3, pp. 285-293;Skipper, N. T., Sposito, G., and Chang, F. R. (1995b), “Monte Carlosimulations of interlayer molecular structure in swelling clayminerals 1. Monolayer Hydrates”, Clays and Clay Minerals, Vol. 43, No.3, pp. 294-303, each incorporated herein by reference in their entirety.They used MONTE (Skipper) software for the purpose. See Skipper, N. T.(1992), “MONTE User's Manual”, Technical Report, Department ofChemistry, University of Cambridge, UK, incorporated herein by referencein its entirety. They explained the methodology and the simulationdetails in two of their consecutive papers (Skipper et al.),respectively. They defined the atomic positions and the correspondingeffective charges of the clay minerals for the simulation purpose. Theoutcome of the study showed that Monte Carlo simulations of theWyoming-type montmorillonite and vermiculite have resulted in layerspacings, average potential energies, and molecular structure that areconsistent with the experimental findings.

Karabomi et al. was one of the early researchers who adopted MD for thenano level simulations. See Karabomi, S., Smit, B., Heidug, W. Urai, E.and van Oort, (1996), “The Swelling of Clays: Molecular Simulations ofthe Hydration of Montmorillonite”, Science, Vol. 271, 23 Feb. 1996,1102-1104, incorporated herein by reference in its entirety. Theyperformed molecular dynamics and Monte Carlo simulations to study thelattice expansion mechanism of the Na-montmorillonite (FIG. 23). Thesimulation results revealed and confirmed the generally accepted theoryof four stable states at lattice basal spacings of 9.7, 12.0, 15.5 and18.3 Å respectively. They also proved that swelling percentages and theswelling sites in the stable form of the Na-montmorillonite aregenerally in good quantitative agreement with the previous studies. Theswelling process resulted in the development of one, three, and thenfive water layers. This anomalous behavior has been found to becontradicting the general concept of formation of hydrated cationslayers of one, two, three, four etc. in Na-montmorillonite. They alsotheorized that relative amount of water adsorbed by Na-montmorilloniteis a result of the balance between the hydrogen bonding between waterand the tetrahedral sheets of the clay and water adsorption in the clayhexagonal cavities. Based on this theory, they defined the stable statesto be those where one of the interaction becomes dominant, while anunstable state to be one where a ‘frustration effect’ is created due tothe predominance of both the phenomena simultaneously. They attributedhigher swelling potential of Na-montmorillonite to this phenomenon.Therefore, a transition would be required from one orientation of watermolecules to a second in order to cause expansion to the clay structure.Clearly, this transition requires lesser free volume of water and isquite easy to take place than the one with the addition of thesimultaneous complete layers of water molecules.

Katti et al. (2005) conducted Molecular Dynamics (MD) study of theinterlayer response of pyrophyllite under the influence of water andcations in the interlayer. See Katti, D. R., Schmidt, S., Ghosh, P., andKatti, K. S., (2005), “Modeling Response of Pyrophyllite Clay Interlayerto Applied Stress Using Steered Molecular Dynamics”, Clays and ClayMinerals, Vol. 52, n2, 171-178, incorporated herein by reference in itsentirety. They used NAMD (Phillips et al.) and VMD software to performinteractive simulations and these were simulated on the North DakotaState University 32 processor parallel computer system. See Phillips, J.C., Braun, R., Wang, W., Gumbart, J., Tajkhorshid, E., Villa, E.,Chipot, C., Skeel, R. D., Kale, L., and Schulten, K (2005), “Scalablemolecular dynamics with NAMD”, Journal of Computational Chemistry,26(16), 1781-1802, incorporated herein by reference in its entirety. Oneof the major parts of the study was to transform the Consistent ForceField (CFF) parameters earlier developed by Teppen et al. to CHARMmforce field parameters. See Teppen, B. J., Rasmussen, K., Bertsch, P.M., Miler, D. M., and Schafer, L. (1997), “Molecular dynamics modelingof clay minerals. 1. Gibbsite, kaolinite, pyrophyllite, and beidellite”,Journal of Physical Chemistry B, 101, 1579-1587, incorporated herein byreference in its entirety. These were later on used with the NAMDsoftware. Basic pyrophyllite model and the force applied model developedby the authors are respectively shown in FIGS. 24 and 25. In this study,forces were applied on the clay surfaces ranging from 0 pN to 160 pNsimulating an equivalent stresses of 0 to 1.65 GPa. The authorsconcluded that deformation of the clay layers observed in this stressrange is only ˜1.6% compared to ˜12.9% for the interlayer. The modulusof the interlayer and the two-clay-layer unit were found to be 13.18 GPaand 54.56 GPa, respectively.

Wang et al. (2007) studied the elastic properties of several mineralsincluding quartz, albite, calcite, montmorillonite, kaolinite andpalygorskite through MD technique. See Wang, J., Sharma A. andGutierrez, S. M. (2007), “Nanoscale Simulations of Rock and ClayMinerals”, ASCE Geotechnical Special Publication 173: Advances inMeasurement and Modeling of Soil Behavior Geo-Denver 2007: New Peaks inGeotechnics, incorporated herein by reference in its entirety. Theymodeled these minerals using both bonded and non-bonded interatomiccontributions. The interatomic bonding energies, used in the molecularsimulation, are expressed in the following Newtonian form as below:

$\begin{matrix}{{m_{i}\frac{d^{2}r_{i}}{{dt}^{2}}} = F_{i}} & \text{2-2}\end{matrix}$

The force F_(i) acting on a particle i is calculated from theinteratomic potential function U (r, r₁, r₂, R_(N) . . . )

$\begin{matrix}{{F_{i} = \frac{\partial{U\left( {r_{1},r_{2},{\ldots\mspace{14mu} r_{N}}} \right)}}{\partial r_{i}}},{i = 1},2,{\ldots\mspace{14mu} N}} & \text{2-3}\end{matrix}$

Dynamics of the system is dominated only by the interatomic potentialfunction U that is representative of the atomic interaction owing to thecomplex quantum effects occurring at the subatomic level. They utilizedthe most commonly adopted pair-wise potentials inclusive ofLennard-Jones (LJ) and Morse potentials, as in the following equations:

$\begin{matrix}{{{U\left( {r_{i},r_{j}} \right)} = {{U(r)} = {4\;{ɛ\left\lbrack {\left( \frac{\sigma}{r} \right)^{12} - \left( \frac{\sigma}{r} \right)^{6}} \right\rbrack}}}},{r = {{r_{ij}} = {{r_{i} - r_{j}}}}},\left( {{LJ}\mspace{14mu}{potential}} \right)} & \text{2-4} \\{{U(r)} = {ɛ{\left\lfloor {e^{2\;{\beta{({\rho - r})}}} - {2\; e^{\beta{({\rho - r})}}}} \right\rfloor.\mspace{14mu}\left( {{Morse}\mspace{14mu}{potential}} \right)}}} & \text{2-5}\end{matrix}$

The potential function used by Sato et al. and Ichikawa et al. for thesimulation of several clay minerals was used to simulate the specificminerals. See Sato, H., Yamagishi, A. and Kawamura, K. (2001),“Molecular simulation for flexibility of a single clay layer”, Journalof Physics Chemistry, vol. B 105, 7990-7997; Ichikawa, Y., Kawamura, K.,Fuji, N. and Nattavut, T. (2002), “Molecular dynamics and multiscalehomogenization analysis of seepage-diffusion problem in bentonite clay”,International Journal of Numerical Methods in Engineering 2002;54:1717-1749, each incorporated herein by reference in their entirety.The function is composed of several potentials such as Coulomb(attractive or repulsive), Born-Mayer-Higgins short range repulsion, vander Waals, and Morse terms. They used TINKER software Ponder forcarrying out MD simulations. See Ponder, J. W. (2011),http://dashermustl.edu/, Washington University, US, incorporated hereinby reference in its entirety. Data input included the initialconfiguration of the atomic structures and the interatomic potentialsassigned to the specific mineral. An NPT (constant number of particlesN, pressure P, and temperature T) ensemble was used to acquire thestress-strain behavior of the simulated minerals. The results of thesimulations as shown in FIG. 26 reveal a general agreement between themeasured and known values of modulli for the minerals except Kaolinite.The authors have attributed the anomalously higher modulus value ofKaolinite to the molecular arrangement at the crystal lattice level.

Wang and Gutierrez (2007) conducted a molecular simulation study ofdehydrated 2:1 clay minerals by changing the MD cell size and shapeunder the general applied stress conditions. See Wang, J., Sharma A. andGutierrez, S. M. (2007), “Nanoscale Simulations of Rock and ClayMinerals”, ASCE Geotechnical Special Publication 173: Advances inMeasurement and Modeling of Soil Behavior Geo-Denver 2007: New Peaks inGeotechnics, incorporated herein by reference in its entirety. Themolecular simulation method adopted by the authors considered the basicrelationship between the atomic level stress tensors, includinginternal, external, and the simulation stress tensor. They thoroughlyinvestigated the relaxation behavior of the dehydrated mica sheets bythe incorporation of varying boundary conditions on the simulation cell.It was concluded that the degree of freedom of the simulation cell isdirectly related to the formation of the final crystal structure. One ofthe important conclusions was the shear deformation of the crystalstructure in the absence of any boundary constraint. They also showedthat the interlayer spacing could either be reduced or completelyremoved by application of the high normal pressures.

Katti et al. (2009) studied the effect of swelling and swelling pressureof the montmorillonite clay using the experimental set up and furthervalidated the results using numerical techniques. See Katti, D. R.,Matar, M. I., Katti, K. S. and Amarasinghe, P. M. (2009), “MultiscaleModeling of Swelling Clays: A Computational and Experimental Approach”,KSCE Journal of Civil Engineering (2009) 13(4): 243-255, incorporatedherein by reference in its entirety. They used a specially designedswelling device to control the swelling and swelling pressure of thesample and studied the clay fabric created at each specified level. Theyconcluded that there is breakdown of the clay particles/assemblages asthe swelling of the clay particles increases as a result of intake ofwater. They used Fourier Transform Infrared Spectroscopy (FTIR) andX-ray diffraction (XRD) techniques to study the microstructure of theswollen clays. They also used Discrete Element Method (DEM) and. SteeredMD based numerical techniques to model the swelling behavior of claysoils. Basic model of Na-montmorillonite with 3 water layers is shown inFIG. 27, while the plots of stress vs. interlayer strain with thevariation of water content is shown in FIG. 29. Based on theexperimental and numerical simulation, main conclusion of their studywas there is increase in d-spacing of the clay particles as a result ofthe swelling and beyond certain d-spacing, particle assemblage breakdowntakes place and more and more particles are exposed to swelling.

Tao et al. performed molecular dynamics simulations to investigate therole of the cations K, Na, and Ca on the stability and swelling ofmontmorillonite. See Tao, L., Xiao-Feng, T., Yu, Z. and Tao, G. (2010),“Swelling of K+, Na+ and Ca2+-montmorillonites and hydration ofinterlayer cations: a molecular dynamics simulation”, Chin. Phys. B Vol.19, No. 10 (2010), incorporated herein by reference in its entirety.They used CLAYFF force field (Cygan et al.) to predict the basal spacingas a function of the water content in the interlayer. See Cygan, R. T.,Liang, J. J. and Kalinichev, A. G. (2004),” Molecular Models ofHydroxide, Oxyhydroxide, and Clay Phases and the Development of aGeneral Force Field, J. Phys. Chem. B 108 1255, incorporated herein byreference in its entirety. All MD simulations were carried out using theLAMMPS software package (Plimpton). See Plimpton, S. J. (1995), “FastParallel Algorithms for Short-Range Molecular Dynamics”, J Comp Phys.,117, 1-19, incorporated herein by reference in its entirety. The resultsof the simulations showed that the swelling pattern of these simulatedMontmorillonite is different than that by the corresponding K+, Na+, andCa2+ montmorillonite (FIG. 29). The authors discovered thatCa-montmorillonite exhibits less swelling than Na- and K-montmorillonitefor a given water content. The results of this study also showed thatthe higher the hydration energy of the interlayer cation, the greater isthis difference. In particular, these results indicated that the valenceof the cations has the larger impact on the behaviour of clay-watersystems.

Katti et al. (2011) presented the results of modeling of molecularinteractions between swelling clay and fluids and their effects on themechanical and flow characteristics. In this study, MD simulations wereconducted to study the possible interactions among clay, water, andcations present in the interlayer using MD based software NAMD (Phillipset al.) and the visualization software VMD (Humphrey et al.). SeeHumphrey, W., Dalke, A., and Schulten, K (1996), “VMD: Visual moleculardynamics”, Journal of Molecular Graphics, 14(1), 33-35, incorporatedherein by reference in its entirety. The results of the study showed anincreased breakdown of the aggregated particles and their correspondingcontributions towards the enhanced swelling and the swelling pressure.Generally, their results showed an agreement with the well-establishedand determined concepts related to the swelling mechanism of the clayminerals. They discovered that the fact that the forces among claysheets and Na+ cations are attractive in nature in the dry state. As pertheir results, these attractive forces/interactions among Na+ and claysurfaces are quite pronounced even up to the presence of 8 water layersin the interlayer and water is still contributing to the attractiveforces among hydrated Na+ cations and the water bounded to the claysurfaces even more than 8 water layers (FIG. 30).

Based on the deliberations above, it could be inferred that nano ormolecular level processes play a central role in the understanding ofthe volume change behavior of the expansive clays. Although some studieshave been conducted to simulate the swelling and/or water absorptionbehavior of the single or isolated expansive clay minerals, modeling ofthe real/natural expansive soil fabric and its interaction with porefluids at molecular level is still lacking. Moreover, no efforts havebeen directed to couple the macro and micro scale material behavior tothe findings of these molecular simulations. Based on all the abovedeliberations on the modeling of expansive clay soils, the following maybe said:

-   -   More effort and emphasis has been directed to the development        and enhancement of the unsaturated non-expansive soils models,        while much lesser effort has been made towards expansive clay        modeling.    -   Almost all the researchers involved in the unsaturated soils        research have considered expansive soils as an extreme case of        the unsaturated soils; rather it should be considered both as a        special case of saturated soils and unsaturated soils under the        complete moisture regime.    -   Micro and nano level fabrics, believed to have a central role in        the overall behavior of expansive clays, are only partially        considered in the modeling concepts. Even the partial        consideration of the micro and nano level fabric is for the        clays compacted/constructed under highly controlled conditions;        natural clay fabrics with multiple clay minerals, silt and sand        inclusions, micro fissures, cementation, over-consolidation,        induration, and other such features have never been considered.    -   The boundary between expansive and non-expansive soils is not        well defined, and more consideration is needed to better        understand the behavior of slightly expansive clay soils such as        broadly graded soils with small Smectite (and Illite) contents        and soil dominated by non-swelling clays such as Kaolinite.    -   Molecular level research, at present, has just concentrated        mostly on one mineral only; interaction with other minerals and        macro particles is lacking.    -   It has been observed that the macroscopic behavior of clay mass        may differ considerably from their nano-scale response, which is        the major motivation for characterizing and modeling these        materials using multiscale simulations.

BRIEF SUMMARY OF THE INVENTION

According to a first aspect, the present disclosure relates to a methodof reducing the swell potential of an expansive clay mineral having awater content and a cation exchange capacity (CEC). The method includes(a) carrying out a forcefield-modified molecular level simulation todetermine an amount of a swelling reduction agent to be incorporatedinto the expansive clay mineral to form a swelling reduction agentincorporated expansive clay mineral with a reduced swell potentialS_(i(ECM)) that is no greater than a pre-set level T, wherein theswelling reduction agent comprises at least one cementation materialselected from the group consisting of calcite, gypsum, and potassiumchloride at a first weight percent of the amount of the swellingreduction agent, and/or at least one exchangeable cation selected fromthe group consisting of K⁺, Ca²⁺ and Mg²⁺ at a second weight percent ofthe amount of the swelling reduction agent, wherein the sum of the firstweight percent and the second weight percent is no greater than 100%,wherein the forcefield-modified molecular level simulation comprisesmolecular mechanics, molecular dynamics, and Monte Carlo simulationtechniques configured to simulate the reduced swell potential S_(i(ECM))of the swelling reduction agent incorporated expansive clay mineralbased on the water content as an initial water content and CEC of theexpansive clay mineral, the at least one cementation material at thefirst weight percent of the amount of the swelling reduction agent,and/or the at least one exchangeable cation at the second weight percentof the amount of the swelling reduction agent, and (b) incorporating theamount of the swelling reduction agent into the expansive clay mineralto form the swelling reduction agent incorporated expansive claymineral.

In one or more embodiments, the CEC of the expansive clay mineral liesin the range of 40-150 meq/100 g dry expansive clay mineral.

In one or more embodiments, the forcefield-modified molecular levelsimulation comprises a modified forcefield according to the followingtable:

Atom Types Atom Atomic Coordi- type Atom mass nation Remarks Na Na22.99000 0 sodium Mg6 + 2 Mg 24.31000 6 magnesium, octahedral, +2oxidation state Al6 Al 26.98150 6 aluminium, octahedral Si3 Si 28.086003 silicon, tetrahedral K_ K 39.94800 0 potassium Ca6 + 2 Ca 40.08000 6calcium, octahedral, +2 oxidation state Diagonal vdw Atom Lennard Radiustype Jones (A) Well depth (kcal/mol) Na LJ_6_12 2.6378 0.1301E+00 Mg6 +2 LJ_6_12 5.9090 0.9029E−06 Al6 LJ_6_12 4.7943 0.1329E−05 Si3 LJ_6_123.7064 0.1841E−05 K_ LJ_6_12 3.7423 0.1000E+00 Ca6 + 2 LJ_6_12 3.39900.2380E+00 Atom typing rules Atom Hybrid- type Atom ization Formaloxidation state Mg6 + 2 Mg 0 0 0 1 Al6 Al 3 0 0 1 Si3 Si 3 0 0 I

In one or more embodiments, the swelling reduction agent comprises theat least one cementation material at the first weight percent of theamount of the swelling reduction agent, and the forcefield-modifiedmolecular level simulation comprises the steps of (i) a molecular levelsimulation of water sorption onto a crystallite of the expansive claymineral to form a water sorbed crystallite of the expansive clay mineralwith the water content of the expansive clay mineral as the initialwater content, (ii) a molecular level simulation of sorption of the atleast one cementation material in an amount proportional to the firstweight percent onto the water sorbed crystallite of the expansive claymineral, (iii) a molecular level simulation of assembling a plurality ofthe water sorbed crystallites of the expansive clay mineral comprisingthe swelling reduction agent to form a loose cubic unit cell and atleast one of a compacted unit cell at a first confining pressure and astress relaxed unit cell at a second confining pressure less than thefirst confining pressure, wherein the loose cubic unit cell, thecompacted unit cell, and the stress relaxed unit cell each comprise Nwater sorbed crystallites of the expansive clay mineral comprising theswelling reduction agent and N is 2-8, and (iv) a molecular levelsimulation of water sorption onto and swelling of the compacted unitcell at the first confining pressure or the stress relaxed unit cell atthe second confining pressure to form a swollen compacted unit cell or aswollen stress relaxed unit cell comprising the N water sorbedcrystallites of the expansive clay mineral comprising the swellingreduction agent until a swell cutoff point is reached, wherein theextent of the swelling of the swollen compacted unit cell or the swollenstress relaxed unit cell comprising the N water sorbed crystallites ofthe expansive clay mineral comprising the swelling reduction agent atthe swell cutoff point corresponds to the reduced swell potentialS_(i(ECM)) of the swelling reduction agent incorporated expansive claymineral.

In one or more embodiments, the swelling reduction agent furthercomprises the at least one exchangeable cation at the second weightpercent of the amount of the swelling reduction agent, and theforcefield-modified molecular level simulation further comprises amolecular level simulation of replacing 0-100% of a total number of atleast one non-K⁺, Ca²⁺, and Mg²⁺ exchangeable cation with the at leastone exchangeable cation at the second weight percent of the amount ofthe swelling reduction agent in the crystallite of the expansive claymineral prior to the molecular level simulation of step (i).

In one or more embodiments, the at least one non-K⁺, Ca²⁺, and Mg²⁺exchangeable cation in the crystallite of the expansive clay mineral isat least one selected from the group consisting of Na⁺ and Li⁺.

In one or more embodiments, the crystallite of the expansive claymineral in the molecular level simulation of step (i) has a size of(13-52)×(27−108)×(10−40) Å.

In one or more embodiments, the molecular level simulations of step (i)and step (iv) comprise a plurality of water sorption phases and 25,000Monte Carlo simulation steps at each water sorption phase.

In one or more embodiments, the loose cubic unit cell comprises N of 3-6water sorbed crystallites with a size of 125×125×125 Å.

In one or more embodiments, the molecular level simulations of step (i)and step (iv) comprise a phase of water sorption in an interlayer spaceof the crystallite of the expansive clay mineral, and the water sorptionin the interlayer space results in a water content of no greater than30% (w/w) in the interlayer space, or an expansion of no greater thanabout 17.5 Å in the interlayer space, or forming no greater than threewater layers in the interlayer space.

In one or more embodiments, the swell cutoff point is reached when aMonte Carlo simulation step during the molecular level simulation ofstep (iv) results in an increase of about 2-4% (w/w) in a water contentof the swollen compacted unit cell or the swollen stress relaxed unitcell comprising the N water sorbed crystallites of the expansive claymineral comprising the swelling reduction agent.

In one or more embodiments, the forcefield-modified molecular levelsimulation further comprises determining a first total cohesive energydensity (TCED1) of the stress relaxed unit cell comprising the N watersorbed crystallites of the expansive clay mineral comprising theswelling reduction agent and a second total cohesive energy density(TCED2) of a stress relaxed unit cell comprising N water sorbedcrystallites of the expansive clay mineral with Na⁺ as the onlyexchangeable cation and without the swelling reduction agent anddetermining (TCED1−TCED2) represented by ΔTCED, wherein the molecularlevel simulation of water sorption onto and swelling of the stressrelaxed unit cell at the second confining pressure in step (iv) furthercomprises determining a third total cohesive energy density (TCED3) ofthe swollen stress relaxed unit cell comprising the N water sorbedcrystallites of the expansive clay mineral comprising the swellingreduction agent and comparing TCED3 with the sum of ΔTCED and a fourthtotal cohesive energy density (TCED4), wherein TCED4 is in the range of3×10⁸-6×10⁸ J/m³, and wherein the swell cutoff point is reached whenTCED3 equals the sum of ΔTCED and the fourth total cohesive energydensity (ΔTCED+TCED4).

In one or more embodiments, the expansive clay mineral is at least oneselected from the group consisting of smectite, bentonite,montmorillonite, beidellite, vermiculite, attapulgite, nontronite,illite, and chlorite.

According to a second aspect, the present disclosure relates to anothermethod of reducing the swell potential of an expansive clay mineralhaving a first water content and a cation exchange capacity (CEC). Themethod includes (a) carrying out a forcefield-modified molecular levelsimulation to determine a second water content of a wetted expansiveclay mineral to be formed by wetting the expansive clay mineral withwater, wherein the forcefield-modified molecular level simulationcomprises molecular mechanics, molecular dynamics, and Monte Carlosimulation techniques configured to simulate a reduced swell potentialS_(w) of the wetted expansive clay mineral that is no greater than apre-set level T based on the cation exchange capacity (CEC) of theexpansive clay mineral and the second water content of the wettedexpansive clay mineral as an initial water content (IWC), wherein thesecond water content as the initial water content (IWC) is greater thanthe first water content but no greater than a final water content (FWC)of the expansive clay mineral when the expansive clay mineral reachesthe swell potential, and (b) wetting the expansive clay mineral withwater to form the wetted expansive clay mineral having the second watercontent and the reduced swell potential S_(w).

In one or more embodiments, the forcefield-modified molecular levelsimulation comprises the steps of (i) a molecular level simulation ofwater sorption onto a crystallite of the expansive clay mineral to forma water sorbed crystallite of the expansive clay mineral with the secondwater content as the initial water content, (ii) a molecular levelsimulation of assembling a plurality of the water sorbed crystallites ofthe expansive clay mineral to form a loose cubic unit cell and at leastone of a compacted unit cell at a first confining pressure and a stressrelaxed unit cell at a second confining pressure less than the firstconfining pressure, wherein the loose cubic unit cell, the compactedunit cell, and the stress relaxed unit cell each comprise N water sorbedcrystallites of the expansive clay mineral and N is 2-8, and (iv) amolecular level simulation of water sorption onto and swelling of thecompacted unit cell at the first confining pressure or the stressrelaxed unit cell at the second confining pressure to form a swollencompacted unit cell or a swollen stress relaxed unit cell comprising theN water sorbed crystallites of the expansive clay mineral until a swellcutoff point is reached, wherein the extent of the swelling of theswollen compacted unit cell or the swollen stress relaxed unit cellcomprising the N water sorbed crystallites of the expansive clay mineralat the swell cutoff point corresponds to the swell potential S_(w) ofthe wetted expansive clay mineral.

In one or more embodiments, the expansive clay mineral is free of acementation material and comprises Na⁺ as the only exchangeable cation,and the molecular level simulation of water sorption onto and swellingof the stress relaxed unit cell at the second confining pressure in step(iv) further comprises determining a dry density and/or a total cohesiveenergy density (TCED) of the swollen stress relaxed unit cell comprisingthe N water sorbed crystallites of the expansive clay mineral, and theswell cutoff point is reached when the dry density of the swollen stressrelaxed unit cell comprising the N water sorbed crystallites of theexpansive clay mineral is in the range of 0.2-0.6 g/cm³, or the TCED ofthe swollen stress relaxed unit cell comprising the N water sorbedcrystallites of the expansive clay mineral is in the range of3×10⁸-6×10⁸ J/m³.

According to a third aspect, the present disclosure relates to a methodof reducing the swell potential of an expansive clayey soil comprisingat least one expansive clay mineral. The proportion of the weight of theat least one expansive clay mineral relative to the total weight of theexpansive clayey soil is P_(ECM). The expansive clayey soil has a watercontent and a cation exchange capacity (CEC). The method includes (a)carrying out a forcefield-modified molecular level simulation todetermine an amount of a swelling reduction agent to be incorporatedinto the expansive clayey soil to form a swelling reduction agentincorporated expansive clayey soil with a reduced swell potentialS_(i(soil)) that is no greater than a pre-set level T*, wherein theswelling reduction agent incorporated expansive clayey soil comprises aswelling reduction agent incorporated at least one expansive claymineral having a swell potential represented by S_(i(ECM)) andS_(i(soil)) equals S_(i(ECM))×P_(ECM), wherein the swelling reductionagent comprises at least one cementation material selected from thegroup consisting of calcite, gypsum, and potassium chloride at a firstweight percent of the amount of the swelling reduction agent, and/or atleast one exchangeable cation selected from the group consisting of K⁺,Ca²⁺, and Mg²⁺ at a second weight percent of the amount of the swellingreduction agent, wherein the sum of the first weight percent and thesecond weight percent is no greater than 100%, wherein theforcefield-modified molecular level simulation comprises molecularmechanics, molecular dynamics, and Monte Carlo simulation techniquesconfigured to simulate the swell potential of the swelling reductionagent incorporated at least one expansive clay mineral S_(i(ECM)) basedon the water content as an initial water content and CEC of theexpansive clayey soil, the at least one cementation material at thefirst weight percent of the amount of the swelling reduction agent,and/or the at least one exchangeable cation at the second weight percentof the amount of the swelling reduction agent, and (b) incorporating theamount of the swelling reduction agent into the expansive clayey soil toform the swelling reduction agent incorporated expansive clayey soil.

In one or more embodiments, the swelling reduction agent comprises theat least one cementation material at the first weight percent of theamount of the swelling reduction agent, and the forcefield-modifiedmolecular level simulation comprises the steps of (i) a molecular levelsimulation of water sorption onto a crystallite of the at least oneexpansive clay mineral to form a water sorbed crystallite of the atleast one expansive clay mineral with the water content of the expansiveclayey soil as the initial water content, (ii) a molecular levelsimulation of sorption of the at least one cementation material in anamount proportional to P_(ECM)×the first weight percent onto the watersorbed crystallite of the at least one expansive clay mineral, (iii) amolecular level simulation of assembling a plurality of the water sorbedcrystallites of the at least one expansive clay mineral comprising theswelling reduction agent to form a loose cubic unit cell and at leastone of a compacted unit cell at a first confining pressure and a stressrelaxed unit cell at a second confining pressure less than the firstconfining pressure, wherein the loose cubic unit cell, the compactedunit cell, and the stress relaxed unit cell each comprise N water sorbedcrystallites of the at least one expansive clay mineral comprising theswelling reduction agent and N is 2-8, and (iv) a molecular levelsimulation of water sorption onto and swelling of the compacted unitcell at the first confining pressure or the stress relaxed unit cell atthe second confining pressure to form a swollen compacted unit cell or aswollen stress relaxed unit cell comprising the N water sorbedcrystallites of the at least one expansive clay mineral comprising theswelling reduction agent until a swell cutoff point is reached, whereinthe extent of the swelling of the swollen compacted unit cell or theswollen stress relaxed unit cell comprising the N water sorbedcrystallites of the at least one expansive clay mineral comprising theswelling reduction agent at the swell cutoff point corresponds to theswell potential of the swelling reduction agent incorporated at leastone expansive clay mineral S_(i(ECM)).

In one or more embodiments, the expansive clayey soil further comprisessand and the method further comprises removing all or a portion of thesand from the expansive clayey soil prior to the incorporating theamount of the swelling reduction agent into the expansive clayey soil toform the swelling reduction agent incorporated expansive clayey soil.

In one or more embodiments, the expansive clayey soil further comprisessand and the method further comprises replacing all or a portion of thesand in the expansive clayey soil with at least one non-expansive claymineral prior to the incorporating the amount of the swelling reductionagent into the expansive clayey soil to form the swelling reductionagent incorporated expansive clayey soil.

The foregoing paragraphs have been provided by way of generalintroduction, and are not intended to limit the scope of the followingclaims. The described embodiments, together with further advantages,will be best understood by reference to the following detaileddescription taken in conjunction with the accompanying drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

A more complete appreciation of the disclosure and many of the attendantadvantages thereof will be readily obtained as the same becomes betterunderstood by reference to the following detailed description whenconsidered in connection with the accompanying drawings, wherein:

FIG. 1A is a graphical presentation of swelling behavior of Sand-Claymixture (El Sohbi and Rabba, 1981).

FIG. 1B is a graphical presentation of swelling behavior of Silt-Claymixture (El Sohbi and Rabba. 1981).

FIG. 2 is a schematic of smectite clay mineral group (Mitchell, 2005).

FIG. 3A is a graphical presentation of micro level clay fabric (Gens andAlonso, 1992).

FIG. 3B is a graphical presentation of macro level clay fabric (Gens andAlonso, 1992).

FIG. 3C is a graphical presentation of platelet level clay fabric (Gensand Alonso, 1992).

FIG. 4A is a graphical presentation of conceptual microstructures forCa²⁺-smectite.

FIG. 4B is a graphical presentation of conceptual microstructures forNa⁺-smectite.

FIG. 4C is a graphical presentation of features of an individualquasicrystal for the quantitative microstructural model (Likos and Lu,2006).

FIGS. 5A, 5B, and 5C are graphical presentations of conceptual fabric ofclayey soils (Sharma, 1998).

FIG. 6 is a graphical presentation of micro and macro level claystructure concept (Sanchez et al., 2005).

FIG. 7 is a graphical presentation of interpretation of diagenesisprocess and structural effects of loading (a, b, and d), unloading (dand c) and reloading (c and e) cycle on a clayey rock (Pinyol et al.,2007).

FIG. 8 is a schematic representation of a desiccated clay soil showingthe differentiation between the unsaturated soil mass and the saturatedsoil elements (Fityus and Buzzy, 2009).

FIG. 9A is an SEM Image of compacted Wyoming bentonite showing bimodalporosity (image obtained parallel to compacted direction).

FIG. 9B is a conceptual diagram of pore spaces on the inter-aggregatescale (Likos and Wayllace, 2010).

FIG. 9C is a conceptual diagram of pore spaces on the intra-aggregatescale (Likos and Wayllace. 2010).

FIG. 9D is a conceptual diagram of pore spaces on the quasicrystal scale(Likos and Wayllace, 2010).

FIG. 9E is a conceptual diagram of pore spaces on the interlayer scale(Likos and Wayllace, 2010).

FIG. 10 is a graphical presentation of forms of water in high-densityclay soil (F, Free or bulk water; E, external or inter-cluster water;Im, inter-lamellar or intra-cluster water; S, Silt; K, Kaolinite; I,Illite; Sm, Smectite) (Hueckel, 1992).

FIG. 11 is a graphical presentation of diffuse Double Layer (DDL)concept (Guoy, 1910 and Chapman, 1913).

FIG. 12. is a graphical presentation of regimes of crystalline andosmotic swelling (Wayllace, 2008).

FIG. 13 is a graphical presentation of hydration process of the clayparticle layers (Wayllace, 2008).

FIG. 14A is a graphical presentation of Load Collapse (LC) yield surfaceconcept (Alonso et al., 1990).

FIG. 14B is a graphical presentation of change in specific volumecorresponding to L1, L2, and L3 according to FIG. 14A (Alonso et al.,1990).

FIG. 14C is a graphical presentation of change in specific volumecorresponding to C1, C2, and C3 according to FIG. 14A (Alonso et al.,1990).

FIGS. 15A, 15B, 15C, and 15D are graphical presentations of elastic zonebounded by Load Collapse (LC) and Suction Increase (SI) curves (Alonsoet al., 1990).

FIG. 16 is a graphical presentation of 3-D yield surfaces in p-q-s space(Alonso et al., 1990).

FIG. 17 is a graphical presentation of neutral line representingmicrostructure in the model (Gens and Alonso, 1992).

FIGS. 18A and 18B are graphical presentations of coupling function inthe expansive clay model (Gens and Alonso, 1992).

FIG. 19 is a graphical presentation of Barcelona Expansive Model (BExM)(Alonso et al., 1999).

FIG. 20 is a graphical presentation of interaction and couplingfunctions in BExM (Alonso et al., 1999).

FIGS. 21A and 21B are graphical presentations of constitutive surfacefor expansive clay in the model (Sanchez et al., 2005).

FIG. 22 is a graphical presentation of coupling functions between macroand micro structure in the model (Sanchez et al., 2005).

FIG. 23 is a graphical presentation of Molecular Simulation of theHydration of Na Montmorillonite (Karaborni et al., 1996).

FIG. 24 is a perspective view of two pyrophyllite layers comprising 2×4unit cells each (Katti et al., 2005).

FIG. 25 is a graphical presentation of forces applied normal to thesimulation cell (Katti et al., 2005).

FIG. 26 is a graphical presentation of modulli values for variousminerals obtained from the Nano-scale modelling (Wang et al., 2007).

FIG. 27 is a snapshot of Na-montmorillonite with 3 water layers in theinterlayer (Katti et al., 2009).

FIG. 28 is a graphical presentation of stress vs. interlayer strainplots for various level of hydration in the interlayer (Katti et al.,2009).

FIG. 29 is a graphical presentation of swelling curves of the potassium,sodium and calcium-montmorillonite clay showing the dependence of thelayer spacing on the water molecules of the clay (Tao et al., 2010).

FIG. 30 is a plot of interaction energies versus number of water layersin the interlayer (Katti et al., 2011).

FIG. 31 is a graphical presentation of Proctor Moisture-Densityrelationships for various bentonite-sand proportioned mixes.

FIG. 32 is a graphical presentation of swell potential test resultsusing laboratory oedometer tests.

FIG. 33 is a graphical presentation of typical crystallite sizedetermination using Scherrer (1918) method.

FIG. 34 is a graphical presentation of typical crystallite unit cell(26×54×20 Å) of Na-montmorillonite with CEC=90 meq/100 g.

FIG. 35 is a graphical presentation of typical crystallite unit cell(26×54×20 Å) of Pyrophyllite with CEC=0.

FIG. 36 is a typical view of water molecule.

FIG. 37 is a typical view of gypsum unit cell.

FIG. 38 is a typical view of calcite unit cell.

FIG. 39 is a graphical presentation of typical initial water sorption ina dry MCEC Na-montmorillonite.

FIG. 40 is a graphical presentation of the final picture of the MCECNa-montmorillonite after sorption of 30% water and the subsequentmolecular dynamics.

FIG. 41 is a graphical presentation of variation in d-spacing of MCECNa-montmorillonite single crystallite during the water sorption process.

FIG. 42 is a graphical presentation of an empty unit cell (54×26×20 Å)by using Sorption module.

FIG. 43 is a graphical presentation of simulation of loose clay mineralsmix showing four water sorbed MCEC Na-montmorillonite crystallitesoccupying random positions in the unit cell by using Sorption module.

FIG. 44 is a graphical presentation of comparison of compaction tomaximum density levels at different confining pressures.

FIG. 45 is a 3-D view of multiple unit cells showing the continuity offabric in the compacted MCEC Na-montmorillonite structure.

FIG. 46 is a graphical presentation of simulation of compaction processof loose crystallites showing compacted crystallites.

FIG. 47 is a graphical presentation of compaction curve showing densitychange with time.

FIG. 48 is a graphical presentation of simulation of stress relief(overconsolidation) showing expanded MCEC Na-montmorillonite structureagainst a stress relief of 0.001 GPa.

FIG. 49 is a graphical presentation of density change during the stressrelief process.

FIG. 50 is a graphical presentation of water sorption simulation in astress relaxed MCEC Na-montmorillonite using Sorption module.

FIG. 51 is a graphical presentation of swelling simulation of watersorbed MCEC Na-montmorillonite showing the expanded structure.

FIG. 52 is a graphical presentation of the swelling curve derived fromthe swelling simulation according to FIG. 51.

FIG. 53 is a graphical presentation of swelling versus moisture contentplot for MCEC Na-montmorillonite compacted at an initial moisturecontent of 30%.

FIG. 54 is a graphical presentation of adsorption of Ca²⁺ and SO₄ ²⁻ onthe individual clay crystallite.

FIG. 55 is a graphical presentation of final fabric of the compactedfour crystallites unit cell after swelling simulation according to FIG.54.

FIG. 56 is a graphical presentation of variation of cohesive energydensity with moisture and density conditions for HCECNa-montmorillonite.

FIG. 57 is a graphical presentation of variation of cohesive energydensity with moisture and density conditions for MCECNa-montmorillonite.

FIG. 58 is a graphical presentation of variation of cohesive energydensity with moisture and density conditions for LCECNa-montmorillonite.

FIG. 59 is a graphical presentation of comparison of d-spacing change ofa single Na-montmorillonite crystallite using original and modified UFF.

FIG. 60 is an ESEM image showing a closed fabric in a post swell samplecomprising 100% bentonite.

FIG. 61 is an ESEM image showing an open fabric in a post swell samplecomprising 30% bentonite and 70% sand.

FIG. 62 is a graphical presentation of analysis of d-spacing incompacted 100% bentonite—dry of OMC showing the XRD pattern.

FIG. 63 is a graphical presentation of analysis of d-spacing incompacted 100% bentonite—dry of OMC showing the d-spacing.

FIG. 64 is a graphical presentation of analysis of d-spacing incompacted 100% bentonite—wet of OMC showing the XRD pattern.

FIG. 65 is a graphical presentation of analysis of d-spacing incompacted 100% bentonite—wet of OMC showing the d-spacing.

FIG. 66 is a graphical presentation of initial stage of sorption ofwater molecules onto montmorillonite crystallite showing Na⁺ cationsurrounded by two water molecules.

FIG. 67 is a graphical presentation of initial stage of sorption ofwater molecules onto montmorillonite crystallite showing a closer viewof Na⁺ cation with sorbed water molecule.

FIG. 68 is a graphical presentation of completely hydrated Na⁺ cationsproviding a general view showing all the cations in the interlayer.

FIG. 69 is a graphical presentation of completely hydrated Na⁺ cationsproviding a close up view of a single hydrated Na⁺ cation.

FIG. 70 is a graphical presentation of interaction of montmorillonitewith calcite.

FIG. 71 is a graphical presentation of interaction of montmorillonitewith gypsum.

FIG. 72 is a graphical presentation of water molecules sorption (10%) tomontmorillonite with 40% Na+60% K.

FIG. 73 is a graphical presentation of water molecules sorption (10%) tomontmorillonite with 40% Na+60% Ca.

FIG. 74 is a graphical presentation of typical fabric ofNa-montmorillonite after compaction at 30% water content.

FIG. 75 is a graphical presentation of typical fabric ofNa-montmorillonite after compaction at 40% water content.

FIG. 76 is a graphical presentation of cohesive energy density plots forcrystallites for all stages of simulations (loose, compacted, relaxed,and swelling) for HCEC.

FIG. 77 is a graphical presentation of cohesive energy density plots forcrystallites for all stages of simulations (loose, compacted, relaxed,and swelling) for MCEC.

FIG. 78 is a graphical presentation of cohesive energy density plots forcrystallites for all stages of simulations (loose, compacted, relaxed,and swelling) for LCEC.

FIG. 79 is a graphical presentation of cohesive energy density plots forcrystallites for all stages of simulations (loose, compacted, relaxed,and swelling) for LCEC (same as FIG. 78 with y scale).

FIG. 80 is a graphical presentation of cohesive energy density plots forcrystallites for all stages of simulations (loose, compacted, relaxed,and swelling) for changes in cementation compounds.

FIG. 81 is a graphical presentation of cohesive energy density plots forcrystallites for all stages of simulations (loose, compacted, relaxed,and swelling) for changes in exchangeable cations.

FIG. 82 is a graphical presentation of the compacted fabric created forNa-montmorillonite at 30% water content using Berendsen barostat.

FIG. 83 is a graphical presentation of the compacted fabric created forNa-montmorillonite at 30% water content using Parrinello barostat.

FIG. 84 is a graphical presentation of a fabric before the stress relieffor Na-montmorillonite.

FIG. 85 is a graphical presentation of a fabric after the stress relieffor Na-montmorillonite.

FIG. 86 is a graphical presentation of typical water molecules sorptionin Na-montmorillonite crystallites compacted at 30% water content, withblue colored water molecules (in the original color figure) indicatingthe sorption in the current sorption step.

FIG. 87 is a graphical presentation of swelling simulation ofcrystallites unit cell of Na-montmorillonite showing pre swell fabric at30% water content.

FIG. 88 is a graphical presentation of swelling simulation ofcrystallites unit cell of Na-montmorillonite showing post swell fabricat 40% water content.

FIG. 89 is a graphical presentation of variation of van der Waalscohesive energy density with initial water content.

FIG. 90 is a graphical presentation of variation of total cohesiveenergy density of Na-montmorillonite crystallites of different CECscompacted at a range of initial water content.

FIG. 91 is a graphical presentation of variation of total cohesiveenergy density of montmorillonite crystallites of LCEC compacted at arange of initial water content.

FIG. 92 is a graphical presentation of variation of total cohesiveenergy density of montmorillonite crystallites of MCEC compacted at arange of initial water content.

FIG. 93 is a graphical presentation of variation of total cohesiveenergy density of montmorillonite crystallites of HCEC compacted at arange of initial water content.

FIG. 94 is a graphical presentation of relationships between totalcohesive energy density and swell potential for different cases ofmontmorillonite with variation in cations and non-clay cementationcompounds.

FIG. 95 is a graphical presentation of 3-D representation ofconstitutive surface of the Nano level model for expansive clays.

FIG. 96 is a graphical presentation of basic relationship between totalcohesive energy density and initial water content.

FIG. 97 is a graphical presentation of variation of initial density withtotal cohesive energy density.

FIG. 98 is a graphical presentation of variation of final density withtotal cohesive energy density.

FIG. 99 is a graphical presentation of variation of final water contentwith the total cohesive energy density.

FIG. 100 is a graphical presentation showing comparison of swellpotential tests results from Hameed (1991) and nano/molecular modelpredictions.

FIG. 101 is a graphical presentation of water content—swell relationshipfor Na-montmorillonite (MCEC).

FIG. 102 is a graphical presentation of water content—swell relationshipfor Na-montmorillonite (HCEC).

FIG. 103 is a graphical presentation of water content—swell relationshipfor 20% Gypsum (MCEC).

FIG. 104 is a graphical presentation of XRD results of dry bentonitesample.

FIG. 105 is a graphical presentation of XRD results of gypsum sample.

FIG. 106 is a graphical presentation of XRD results of Calcium Carbonatesample.

FIG. 107 is a graphical presentation of XRD results of kaolinite sample.

FIG. 108 is a graphical presentation of XRD results of sand sample.

FIG. 109 is a graphical presentation of XRD Results of 100% bentonitecompacted on dry of OMC—pre swell conditions.

FIG. 110 is a graphical presentation of XRD Results of 100% bentonitecompacted on dry of OMC—post swell conditions.

FIG. 111 is a graphical presentation of XRD Results of 100% bentonitecompacted on wet of OMC—pre swell conditions.

FIG. 112 is a graphical presentation of XRD Results of 100% bentonitecompacted on wet of OMC—post swell conditions.

FIG. 113 is a graphical presentation of XRD Results of 30%, bentonite,50% Calcite, and 20% Sand compacted on dry of OMC—pre swell conditions.

FIG. 114 is a graphical presentation of XRD Results of 30% bentonite,50% Calcite, and 20% Sand compacted on dry of OMC—post swell conditions.

FIG. 115 is a graphical presentation of XRD Results of 30% bentonite,50% Gypsum, and 20% Sand compacted on dry of OMC—pre swell conditions.

FIG. 116 is a graphical presentation of XRD Results of 30% bentonite,50% gypsum, and 20% sand compacted on dry of OMC—post swell conditions.

FIG. 117 is a graphical presentation of XRD Results of 30% bentonite,static compaction on dry of OMC—pre swell conditions.

FIG. 118 is a graphical presentation of XRD Results of 30% bentonite,static compaction on dry of OMC—post swell conditions.

FIG. 119 is a graphical presentation of XRD Results of 30% bentonite,30% calcite, and 40% sand compacted on dry of OMC—pre swell conditions.

FIG. 120 is a graphical presentation of XRD Results of 30% bentonite,30% calcite, and 40% sand compacted on dry of OMC—post swell conditions.

FIG. 121 is a graphical presentation of XRD Results of 30% bentonite,30% kaolinite, and 40% sand compacted on dry of OMC—pre swellconditions.

FIG. 122 is a graphical presentation of XRD Results of 30% bentonite,30% kaolinite, and 40% sand compacted on dry of OMC—post swellconditions.

FIG. 123 is a graphical presentation of XRD Results of 60% bentonite and40% sand compacted on dry of OMC—pre swell conditions.

FIG. 124 is a graphical presentation of XRD Results of 60%, bentoniteand 40% sand compacted on dry of OMC—post swell conditions.

FIG. 125 is a graphical presentation of XRD Results of 60% bentonite,and 40% sand compacted on wet of OMC—pre swell conditions.

FIG. 126 is a graphical presentation of XRD Results of 60% Bentonite and40% Sand compacted on wet of OMC—post swell conditions.

FIG. 127 is a graphical presentation of XRD Results of Qatif-1 sample atNMC—pre swell conditions.

FIG. 128 is a graphical presentation of XRD Results of Qatif-1 sample atNMC—post swell conditions.

FIG. 129 is a graphical presentation of XRD Results of 10% Bentonite and90% Sand compacted on wet of OMC—pre swell conditions.

FIG. 130 is a graphical presentation of XRD Results of 10% Bentonite and90% Sand compacted on wet of OMC—post swell conditions.

FIG. 131 is a graphical presentation of XRD Results of 30% Bentonite,30% Gypsum, and 40% Sand compacted on dry of OMC—pre swell conditions.

FIG. 132 is a graphical presentation of XRD Results of 30% Bentonite,30% Gypsum, and 40% Sand compacted on dry of OMC—post swell conditions.

FIG. 133 is a graphical presentation of XRD Results of 30% Bentonite and70% Sand compacted on wet of OMC—pre swell conditions.

FIG. 134 is a graphical presentation of XRD Results of 30% Bentonite and70% Sand compacted on wet of OMC—post swell conditions.

FIG. 135 is a graphical presentation of XRD Results of Qatif-2 sample atNMC—pre swell conditions.

FIG. 136 is a graphical presentation of XRD Results of Qatif-2 sample atNMC—post swell conditions.

FIG. 137 is a graphical presentation of XRD Results ofNa-montmorillonite from The Clay Minerals Society compacted on dry ofOMC—pre swell conditions.

FIG. 138 is a graphical presentation of XRD Results ofNa-montmorillonite from The Clay Minerals Society compacted on dry ofOMC—post swell conditions.

FIG. 139 is a graphical presentation of XRD Results ofCa-montmorillonite from The Clay Minerals Society compacted on dry ofOMC—pre swell conditions.

FIG. 140 is a graphical presentation of XRD Results ofCa-montmorillonite from The Clay Minerals Society compacted on dry ofOMC—post swell conditions.

FIG. 141 is a graphical presentation of FTIR results of dry Bentonitesample.

FIG. 142 is a graphical presentation of FTIR results of CalciumCarbonate sample.

FIG. 143 is a graphical presentation of FTIR results of Gypsum sample.

FIG. 144 is a graphical presentation of FTIR results of Sand sample.

FIG. 145 is a graphical presentation of FTIR results of Kaolinitesample.

FIG. 146 is a graphical presentation of comparison of FTIR results ofdry Bentonite and at various moisture contents from 10% to 60%.

FIG. 147 is a graphical presentation of FTIR results of 100% Bentonitecompacted on dry of OMC—pre swell conditions.

FIG. 148 is a graphical presentation of FTIR results of 100% Bentonitecompacted on dry of OMC—post swell conditions.

FIG. 149 is a graphical presentation of FTIR results of 60% Bentoniteand 40% Sand compacted on dry of OMC—pre swell conditions.

FIG. 150 is a graphical presentation of FTIR results of 60% Bentoniteand 40% Sand compacted on dry of OMC—post swell conditions.

FIG. 151 is a graphical presentation of FTIR results of 30% Bentoniteand 70% Sand compacted on dry of OMC—pre swell conditions.

FIG. 152 is a graphical presentation of FTIR results of 30% Bentoniteand 70% Sand compacted on thy of OMC—post swell conditions.

FIG. 153 is a graphical presentation of FTIR results of Qatif-2 sampleat NMC—pre swell conditions.

FIG. 154 is a graphical presentation of FTIR results of Qatif-2 sampleat NMC—post swell conditions.

FIG. 155 is a graphical presentation of FTIR results of 30% Bentonite,30% Gypsum, and 40% Sand compacted on dry of OMC—pre swell conditions.

FIG. 156 is a graphical presentation of FTIR results of 30% Bentonite,30% Gypsum, and 40% Sand compacted on dry of OMC—post swell conditions.

FIG. 157 is a graphical presentation of FTIR results of 30% Bentonite,50% Gypsum, and 20% Sand compacted on dry of OMC—pre swell conditions.

FIG. 158 is a graphical presentation of FTIR results of 30% Bentonite,50% Gypsum, and 20% Sand compacted on dry of OMC—post swell conditions.

FIG. 159 is a graphical presentation of FTIR results of 30% Bentonite,10% Gypsum, and 60% Sand compacted on dry of OMC—pre swell conditions.

FIG. 160 is a graphical presentation of FTIR results of 30% Bentonite,10% Gypsum, and 60% Sand compacted on dry of OMC—post swell conditions.

FIG. 161 is a graphical presentation of FTIR results of 30% Bentonite,30% Calcite, and 40% Sand compacted on dry of OMC—pre swell conditions.

FIG. 162 is a graphical presentation of FTIR results of 30% Bentonite,30% Calcite, and 40% Sand compacted on dry of OMC—post swell conditions.

FIG. 163 is a graphical presentation of FTIR results of 30% Bentonite,50% Calcite, and 20% Sand compacted on dry of OMC—pre swell conditions.

FIG. 164 is a graphical presentation of FTIR results of 30% Bentonite,50% Calcite, and 20% Sand compacted on dry of OMC—post swell conditions.

FIG. 165 is a graphical presentation of FTIR results of 30% Bentonite,30% Kaolinite, and 40% Sand compacted on dry of OMC—pre swellconditions.

FIG. 166 is a graphical presentation of FTIR results of 30% Bentonite,30% Kaolinite, and 40% Sand compacted on dry of OMC—post swellconditions.

FIG. 167 is a graphical presentation of FTIR results of 10% Bentoniteand 90% Sand compacted on wet of OMC—pre swell conditions.

FIG. 168 is a graphical presentation of FTIR results of 10% Bentoniteand 90% Sand compacted on wet of OMC—post swell conditions.

FIG. 169 is an ESEM image of 100% Bentonite compacted on dry of OMC—preswell.

FIG. 170 is a graphical presentation of EDS of general area of ESEM inFIG. 169.

FIG. 171 is an ESEM image of 100% Bentonite compacted on dry of OMC—preswell.

FIG. 172 is an ESEM image of 100% Bentonite compacted on dry of OMC—postswell.

FIG. 173 is an ESEM image of 100% Bentonite compacted on wet of OMC—preswell.

FIG. 174 is an ESEM image of 100% Bentonite compacted on wet of OMC—postswell.

FIG. 175 is a graphical presentation of EDS of 100% Bentonite compactedon dry of OMC—pre swell.

FIG. 176 is a graphical presentation of EDS of 100% Bentonite compactedon thy of OMC—post swell.

FIG. 177 is a graphical presentation of EDS of 100% Bentonite compactedon wet of OMC—pre swell.

FIG. 178 is a graphical presentation of EDS of 100% Bentonite compactedon dry of OMC—post swell.

FIG. 179 is an ESEM image of dry Bentonite sample.

FIG. 180 is a graphical presentation of EDS of dry Bentonite sample.

FIG. 181 is an ESEM image of Qatif-2 sample—pre swell.

FIG. 182 is a graphical presentation of EDS of Qatif-2 sample—pre swell.

FIG. 183 is an ESEM image of 30% Bentonite and 70% Sand—Dry of OMC—Preswell.

FIG. 184 is an ESEM image of 30% Bentonite and 70% Sand—Dry of OMC—Postswell.

FIG. 185 is an ESEM image of 30% Bentonite and 70% Sand—Dry of OMC—Preswell.

FIG. 186 is an ESEM image of 30% Bentonite and 70% Sand—Dry of OMC—Postswell.

FIG. 187 is an ESEM image of of 30% Bentonite, 70% Sand-Static-Dry ofOMC—Pre swell.

FIG. 188 is an ESEM image of 30% Bentonite, 70% Sand-Static-Dry ofOMC—Post swell.

FIG. 189 is an ESEM image of 30% Bentonite, 70% Sand-Static-Dry ofOMC—Pre swell.

FIG. 190 is an ESEM image of 30% Bentonite, 70% Sand-Static-Dry ofOMC—Post swell.

FIG. 191 is an ESEM image of 30% Bentonite, 10% Gypsum, 60% Sand-Dry ofOMC—Pre swell.

FIG. 192 is an ESEM image of 30% Bentonite, 10% Gypsum, 60% Sand-Dry ofOMC—Post swell.

FIG. 193 is a graphical presentation of EDS of 30% Bentonite, 10%Gypsum, 60% Sand-Dry of OMC—Pre swell.

FIG. 194 is a graphical presentation of EDS of 30% Bentonite, 10%Gypsum, 60% Sand-Dry of OMC—Post swell.

FIG. 195 is an ESEM image of 30% Bentonite, 30% Gypsum, 40% Sand-Dry ofOMC—Pre swell.

FIG. 196 is an ESEM image of 30% Bentonite, 30% Gypsum, 40% Sand-Dry ofOMC—Post swell.

FIG. 197 is an ESEM image of 30% Bentonite, 30% Gypsum, 40% Sand-Dry ofOMC—Post swell.

FIG. 198 is a graphical presentation of EDS of 30% Bentonite, 30%Gypsum, 40% Sand-Dry of OMC—Post swell.

FIG. 199 is an ESEM image of 30% Bentonite, 30% Calcite, 40% Sand-Dry ofOMC—Pre swell.

FIG. 200 is an ESEM image of 30% Bentonite, 30% Calcite, 40% Sand-Dry ofOMC—Post swell.

FIG. 201 is a graphical presentation of EDS of 30% Bentonite, 30%Calcite, 40% Sand-Dry of OMC—Pre swell.

FIG. 202 is a graphical presentation of EDS of 30% Bentonite, 30%Calcite, 40% Sand-Dry of OMC—Post swell.

FIGS. 203A, 203B, and 203C are Micro CT Scans of Kaolinite-SandCompacted Specimens (Pre Swelling).

FIGS. 204A, 204B, and 204C are Micro CT Scans of Kaolinite-SandCompacted Specimens (Post Swelling).

FIGS. 205A, 205B, and 205C are Micro CT Scans of Na-Montmorillonite-SandCompacted Specimens (Pre Swelling).

FIGS. 206A, 206B, and 206C are Micro CT Scans of Na-montmorillonite-SandCompacted Specimens (Post Swelling).

FIGS. 207A, 207B, and 207C are Micro CT Scans of Ca-montmorillonite-SandCompacted Specimens (Pre Swelling).

FIGS. 208A, 208B, and 208C are Micro CT Scans of Ca-montmorillonite-SandCompacted Specimens (Post Swelling).

FIGS. 209A and 209B are Micro CT Scans of Qatif-1 Specimens (Pre andPost Swelling).

FIG. 210 is a graphical presentation of molecular simulation resultshowing Water sorbed single crystallite of Na-montmorillonite MCEC atinitial water content=40%.

FIG. 211 is a graphical presentation of molecular simulation resultshowing Loose mix simulation of Na-montmorillonite MCEC at initial watercontent=40%.

FIG. 212 is a graphical presentation of molecular simulation resultshowing compacted unit cell of Na-montmorillonite MCEC at initial watercontent=40%.

FIG. 213 is a graphical presentation of compaction plot of unit cell ofNa-montmorillonite MCEC at initial water content=40%.

FIG. 214 is a graphical presentation of molecular simulation resultshowing stress relaxation of the unit cell of Na-montmorillonite MCEC atinitial water content=40%.

FIG. 215 is a graphical presentation of stress relaxation plot of theunit cell of Na-montmorillonite MCEC at 40% water content.

FIG. 216 is a graphical presentation of molecular simulation resultshowing 10% water sorption in Na-montmorillonite MCEC crystallites unitcell (initial water content=40%).

FIG. 217 is a graphical presentation of molecular simulation resultshowing single crystallite of Na-montmorillonite HCEC at initial watercontent=30%.

FIG. 218 is a graphical presentation of molecular simulation resultshowing loose arrangement of crystallites of Na-montmorillonite HCEC atinitial moisture content=30%.

FIG. 219 is a graphical presentation of molecular simulation resultshowing compacted unit cell of Na-montmorillonite HCEC at initial watercontent=30%.

FIG. 220 is a graphical presentation of molecular simulation resultshowing stress relaxed unit cell of Na-montmorillonite HCEC at initialwater content=30°/o.

FIG. 221 is a graphical presentation of molecular simulation resultshowing single crystallite of montmorillonite (60% Ca+40% Na) at initialwater content=10%.

FIG. 222 is a graphical presentation of molecular simulation resultshowing loose mix of four montmorillonite crystallites (60% Ca+40% Na)at initial moisture content=10%.

FIG. 223 is a graphical presentation of molecular simulation resultshowing compacted four montmorillonite crystallites (60% Ca+40 Na) atinitial moisture content=10%.

FIG. 224 is a graphical presentation of molecular simulation resultshowing single Na-montmorillonite crystallite MCEC at initial moisturecontent=10%).

FIG. 225 is a graphical presentation of molecular simulation resultshowing four Na-montmorillonite crystallites MCEC at initial moisturecontent=10%.

FIG. 226 is a graphical presentation of molecular simulation resultshowing four compacted Na-montmorillonite crystallites MCEC at initialmoisture content=10%.

FIG. 227 is a graphical presentation of an embodiment of a specialpurpose computer for performing the molecular level simulation.

DETAILED DESCRIPTION OF THE EMBODIMENTS

According to a first aspect, the present disclosure relates to a methodof reducing the swell potential of an expansive clay mineral having awater content and a cation exchange capacity (CEC). The method includes(a) carrying out a forcefield-modified molecular level simulation todetermine an amount of a swelling reduction agent to be incorporatedinto the expansive clay mineral to form a swelling reduction agentincorporated expansive clay mineral with a reduced swell potentialS_(i(ECM)) that is no greater than a pre-set level T, wherein theswelling reduction agent comprises at least one cementation materialselected from the group consisting of calcite, gypsum, and potassiumchloride at a first weight percent of the amount of the swellingreduction agent, and/or at least one exchangeable cation selected fromthe group consisting of K⁺, Ca²⁺, and Mg²⁺ at a second weight percent ofthe amount of the swelling reduction agent, wherein the sum of the firstweight percent and the second weight percent is no greater than 100%,wherein the forcefield-modified molecular level simulation comprisesmolecular mechanics, molecular dynamics, and Monte Carlo simulationtechniques configured to simulate the reduced swell potential S_(i(ECM))of the swelling reduction agent incorporated expansive clay mineralbased on the water content as an initial water content and CEC of theexpansive clay mineral, the at least one cementation material at thefirst weight percent of the amount of the swelling reduction agent,and/or the at least one exchangeable cation at the second weight percentof the amount of the swelling reduction agent, and (b) incorporating theamount of the swelling reduction agent into the expansive clay mineralto form the swelling reduction agent incorporated expansive claymineral.

Expansive clay mineral is a type of clay mineral that is known as alightweight aggregate with a rounded structure, with a porous inner, anda resistant and hard outer layer. An expansive clay mineral or anexpansive clayey soil comprising one or more expansive clay minerals isprone to large volume changes (swelling and shrinking) that are directlyrelated to changes in water content. Smectite, montmorillonite, andbentonite clay minerals or an expansive clayey soil comprising smectite,montmorillonite, and bentonite clay minerals have the most dramaticshrink-swell capacity. An expansive clay mineral or an expansive clayeysoil can swell in a wet season and shrink and form cracks in a dryseason. A laboratory test to measure the swell potential of an expansiveclay mineral or an expansive clayey soil is ASTM D 4829, or morepreferably ASTM D 5890. For example, an expansive clay mineral sample ora compacted or a natural undisturbed expansive clayey soil sample may besubjected to free swell testing in the presence of water in an oedometertest equipment. Increase in height of the sample is recorded at regulartime intervals until no further noticeable change in height of thesample is recorded. Maximum change in the height of the sample dividedby the original height is recorded and expressed in percent swell forthe tested sample.

In some embodiments, the expansive clay mineral is one selected from thegroup consisting of smectite, bentonite, montmorillonite, beidellite,vermiculite, attapulgite, nontronite, illite, and chlorite.

An expansive clay mineral or an expansive clayey soil comprising one ormore expansive clay minerals swells or shrinks when there is a change inwater content. In the disclosed method, the water content of theexpansive clay mineral or the expansive clayey soil, if not known, maybe determined according to ASTM D 2216—Standard Test Method forLaboratory Determination of Water (Moisture) Content of Soil, Rock, andSoil-Aggregate Mixtures. The water content is the ratio, expressed as apercentage, of the mass of “pore” or “free” water in a given mass ofclay mineral or soil to the mass of the dry clay mineral or soil solids.The following are the procedures of an exemplary clay mineral or soilwater content test: (1) determining and recording the mass of an empty,clean, and dry moisture can with its lid represented by M_(c) using abalance; (2) placing the moist clay mineral or soil sample in themoisture can, securing the lid of the moisture can, and determining andrecording the mass of the moisture can containing the moist clay mineralor soil sample with the lid represented by M_(cms); (3) placing andleaving the moisture can containing the moist clay mineral or soilsample with the lid removed in a drying oven that is set at 100-110° C.overnight; (4) removing the moisture can from the oven, and allowing themoisture can to cool to room temperature after carefully and securelyreplacing the lid of the moisture can on the moisture can, preferablyusing gloves; and (5) determining and recording the mass of the moisturecan containing the dry clay mineral or soil sample and the lidrepresented by M_(cds) using a balance. The water content of the claymineral or soil sample is calculated according to the followingequation:

$W = {\frac{Mw}{Ms} \times 100}$where Ms is the mass of soil solids and Ms=Mcds−Mc; and Mw is the massof pore water and Mw=Mcms−Mcds.

The cation exchange capacity (CEC) of an expansive clay mineral or anexpansive clayey soil is the number of exchangeable cations per dryweight that the expansive clay mineral or the expansive clayey soil iscapable of holding, at a given pH value, and available for exchange withthe expansive clay mineral water solution or the expansive clayey soilwater solution. It is expressed as milliequivalent of hydrogen per 100 gof dry clay mineral or soil (meq+/100 g), or the SI unit centi-mol perkg (cmol+/kg). The expansive clay minerals, and in the expansive clayeysoil, also non-expansive clay minerals and humus have electrostaticsurface charges that attract and hold ions. The holding capacity of aclay mineral varies with the type of the clay mineral. Humus has a CECthat is two to three times that of the best clay mineral. For manyexpansive clay minerals and expansive clayey soils, the CEC is dependentupon the pH of the expansive clay mineral or the expansive clayey soil.As expansive clay mineral or expansive clayey soil acidity increases (pHdecreases), more H⁺ ions are attached to the expansive clay mineral orexpansive clayey soil colloids, pushing the other cations from theexpansive clay mineral or expansive clayey soil colloids and into theexpansive clay mineral or expansive clayey soil water solution.Inversely, when an expansive clay mineral or an expansive clayey soilbecomes more basic (pH increases), the available cations in theexpansive clay mineral or expansive clayey soil water solution decreasesbecause there are fewer H⁺ ions to push cations into the expansive claymineral or expansive clayey soil water solution from the expansive claymineral or expansive clayey soil colloids (CEC increases). In thedisclosed method, the CEC of the expansive clay mineral or the expansiveclayey soil may be determined by two standardized International SoilReference and Information Centre methods: extraction with ammoniumacetate; and the silver-thiourea method (one-step centrifugalextraction). The CEC of an expansive clay mineral or an expansive clayeysoil, if not known, may be preferably determined according to the methoddisclosed by Rayment and Higginson, Electrical Conductivity, In“Australian Laboratory Handbook of Soil and Water Chemical Methods,”Inkata Press: Melbourne, 1992, incorporated herein by reference in itsentirety. In some embodiments, the CEC of the expansive clay mineral orthe expansive clayey soil is in the range of 30-250 meq/100 g, 40-150meq/100 g, 60-120 meq/100 g, or 80-100 meq/100 g. In some embodiments,the water content of the expansive clay mineral or the expansive clayeysoil is in the range of 5-100% (w/w), 10-90% (w/w), 20-80% (w/w), 30-70%(w/w), or 40-60% (w/w).

The swelling reduction agent used by the disclosed method preferablyincludes, without limitation, cementation materials, such as calcite,gypsum, and potassium chloride, and exchangeable cations of K⁺, Ca²⁺,and Mg²⁺, and combinations thereof.

Calcite is a carbonate mineral and the most stable polymorph of calciumcarbonate (CaCO₃). All forms of calcite, such as fibrous, granular,lamellar, and/or compact calcite, and either highly pure or calcite withimpurities may be used. Calcite can be either dissolved by groundwateror precipitated by groundwater, depending on several factors includingthe water temperature, pH, and dissolved ion concentrations. Calcite isfairly insoluble in cold water, and exhibits an unusual characteristiccalled retrograde solubility in which it becomes less soluble in wateras the temperature increases. To increase the incorporation of calciteinto an expansive clay mineral or an expansive clayey soil through, forexample, absorption and/or adsorption, the pH of the expansive claymineral or the expansive clayey soil is preferably acidic, e.g. a pH of1-6, preferably a pH of 1-4, or preferably a pH of 2-3, and thetemperature of the expansive clay mineral or the expansive clayey soilis preferably at a low ambient temperature of 4-30° C., preferably10-25° C., or more preferably 15-20° C. In some embodiments, calcite isincorporated into the expansive clay mineral or the expansive clayeysoil by mixing calcite particles with the expansive clay mineral or theexpansive clayey soil and/or by depositing a layer of calcite particleson the surface of the expansive clay mineral or the expansive clayeysoil to let the expansive clay mineral or the expansive clayey soilabsorb and/or adsorb calcite from the expansive clay mineral orexpansive clayey soil water solution. In other embodiments, calcite isincorporated into the expansive clay mineral or the expansive clayeysoil by microbiologically induced calcium carbonate precipitation,whereby photosynthetic microorganisms such as cyanobacteria andmicroalgae; sulfate-reducing bacteria; and some species ofmicroorganisms involved in nitrogen cycle produce calcium carbonatethrough autotrophic and heterotrophic pathways and induce calciumcarbonate precipitation within the expansive clay mineral or expansiveclayey soil matrix. Calcite reduces the swell potential of the expansiveclay mineral or the expansive clayey soil probably by providing bindingor cementation effects to the individual or group of the expansive claymineral particles.

Gypsum is a soft sulfate mineral composed of calcium sulfate dihydrate,with the chemical formula CaSO₄.2H₂O. Gypsum is moderately water-soluble(˜2.0-2.5 g/L at 25° C.) and, in contrast to most other salts, exhibitsretrograde solubility, becoming less soluble at higher temperatures.Thus, to increase the incorporation of gypsum into an expansive claymineral or an expansive clayey soil through, for example, absorptionand/or adsorption, the expansive clay mineral or the expansive clayeysoil is preferably at a low ambient temperature of 4-30° C., preferably10-25° C., or more preferably 15-20° C. to facilitate dissolution ofgypsum in the expansive clay mineral water solution or the expansiveclayey soil water solution. In one embodiment, the gypsum used is puregypsum that has a white color, i.e. white gypsum. In another embodiment,the gypsum used is gypsum with impurities that has a wide range ofcolors, including red gypsum. Red gypsum or secondary gypsum istypically comprised predominantly of calcium sulfate in varying statesof hydration, along with oxides of iron in an amount varying from about3-35%, and various trace elements. Red gypsum may be produced as anindustrial by-product, for example, in the manufacture of titaniumdioxide pigment via the well-known sulfate process, in which it isprecipitated from acidic solution filtrates. Incorporation of red gypsuminto an expansive clay mineral or an expansive clayey soil may alsoincrease the plastic limit and reduce frost susceptibility of theexpansive clay mineral or the expansive clayey soil. In still anotherembodiment, the gypsum used is a mixture of white gypsum, red gypsum,and/or one or more other types of impure gypsum. Gypsum may beincorporated into the expansive clay mineral or the expansive clayeysoil by spraying a gypsum water solution onto the expansive clay mineralor the expansive clayey soil, soaking the expansive clay mineral or theexpansive clayey soil in a gypsum water solution, injecting a gypsumwater solution into the expansive clay mineral or the expansive clayeysoil, mixing gypsum particles with the expansive clay mineral or theexpansive clayey soil, depositing a layer of gypsum particles on thesurface of the expansive clay mineral or the expansive clayey soil tolet the expansive clay mineral or the expansive clayey soil absorb andor adsorb gypsum from the expansive clay mineral or expansive clayeysoil water solution. Since gypsum has a higher solubility in water thancalcite, in practice using gypsum as a swelling reduction agentadvantageously results in a greater reduction in the swell potential ofthe expansive clay mineral or the expansive clayey soil than using anequivalent amount of calcite. The concentration of the gypsum watersolution may be 0.5-2.5 g/L, 1-2 g/L, or 1.5 g/L. Like calcite, gypsumreduces the swell potential of the expansive clay mineral or theexpansive clayey soil probably by providing binding or cementationeffects to the individual or group of the expansive clay mineralparticles.

Since potassium chloride dissolves readily in water, incorporation ofpotassium chloride into an expansive clay mineral or an expansive clayeysoil can be accomplished by spraying a KCl water solution onto theexpansive clay mineral or the expansive clayey soil, soaking theexpansive clay mineral or the expansive clayey soil in a KCl watersolution, injecting a KCl water solution into the expansive clay mineralor the expansive clayey soil, mixing solid KCl particles with theexpansive clay mineral or the expansive clayey soil, depositing a layerof solid KCl particles on the surface of the expansive clay mineral orthe expansive clayey soil to let the expansive clay mineral or theexpansive clayey soil absorb and/or adsorb KCl from the expansive claymineral or expansive clayey soil water solution. The concentration ofthe KCl water solution may be 10-400 g/L, 50-300 g/L, or 100-200 g/L.Similar to calcite and gypsum, KCl reduces the swell potential of theexpansive clay mineral or the expansive clayey soil probably due to abinding or cementation effect it provides to the expansive clay mineralparticles, in addition to its cation exchange capability of replacing anon-K⁺ cation in the expansive clay mineral particles with K⁺, dependingon the amount of KCl the expensive clay mineral particles are exposedto, and/or the amount of KCl incorporated into the expansive claymineral particles. The cementation effect of KCl is achieved bydissolution of KCl in water to produce K⁺ and Cl⁻ and sorption of K⁺ andCl⁻ onto the expansive clay mineral crystallites, creating electrostaticfields to bind the expansive clay mineral crystallites.

Exchangeable K⁺, Ca²⁺, and/or Mg²⁺ may be provided by an aqueoussolution comprising exchangeable K⁺, Ca²⁺, and/or Mg²⁺, by suitablesolid potassium, calcium, and/or magnesium salt particles, or by a K⁺,Ca²⁺, and/or Mg²⁺ loaded exchange resin to replace certain cations in anexpansive clay mineral or an expansive clayey soil, e.g. Na⁺ and Li⁺,with K⁺, Ca²⁺, and/or Mg²⁺. Non-limiting examples of suitable potassiumsalts in either solid particle form or an aqueous solution providingexchangeable K⁺ to the expansive clay mineral or the expansive clayeysoil include K₂CO₃, KNO₂, KNO₃, KHSO₄, K₂SO₄, K₂HPO₄, K₃PO₄, and KCl.Non-limiting examples of suitable calcium salts in either solid particleform or an aqueous solution providing exchangeable Ca²⁺ to the expansiveclay mineral or the expansive clayey soil include CaCl₂, Ca(NO₃)₂, andCa(MnO₄)₂. Non-limiting examples of suitable magnesium salts in eithersolid particle form or an aqueous solution providing exchangeable Mg²⁺to the expansive clay mineral or the expansive clayey soil includeMgCl₂, MgSO₄, and Mg(NO₃)₂. A suitable K⁺, Ca²⁺, and/or Mg²⁺ loadedexchange resin may be a strong acid type of cation resin, e.g. one witha sulfonic acid ionizable group, or a weak acid type of cation resin,e.g. one with a carboxylic acid ionizable group, depending on the pH ofthe expansive clay mineral or the expansive clayey soil the K⁺, Ca²⁺,and/or Mg²⁺ loaded exchange resin is applied to.

Since the CEC of the expansive clay mineral or the expansive clayey soilis generally dependent on the pH of the expansive clay mineral or theexpansive clayey soil, with the expansive clay mineral or the expansiveclayey soil having a higher CEC at a more basic pH, in some embodiments,the pH of the expansive clay mineral or the expansive clayey soil isadjusted to 8-14, 9-13, or 10-12 by, for example, NaOH, KOH, and/or limeprior to incorporating the swelling reduction agent comprisingexchangeable K⁺, Ca²⁺, and/or Mg²⁺ into the expansive clay mineral orthe expansive clayey soil. When the exchangeable K⁺, Ca²⁺, and/or Mg²⁺are in an aqueous solution, the exchangeable K⁺, Ca²⁺, and/or Mg²⁺ maybe incorporated into the expansive clay mineral or the expansive clayeysoil by spraying the aqueous solution onto the expansive clay mineral orthe expansive clayey soil, soaking the expansive clay mineral or theexpansive clayey soil in the aqueous solution, and/or injecting theaqueous solution into the expansive clay mineral or the expansive clayeysoil. When an ion exchange resin comprising exchangeable K⁺, Ca²⁺,and/or Mg²⁺ is used, the resin particles may be batch mixed with theexpansive clay mineral or the expansive clayey soil. Alternatively, theresin particles may be first packed in resin bags made of, for example,a piece of porous nylon fabric and then the resin bags may be mixed withthe expansive clay mineral or the expansive clayey soil. The resin bagsmay vary in size, for example, from small ones holding only a few gramsof resin to others several centimeters in diameter, depending on thevolume of the expansive clay mineral or the expansive clayey soil to betreated and the desired efficiency of the contact of the resin particleswith the expansive clay mineral or the expansive clayey soil. Orpreferably, the ion exchange resin is modified and shaped as a membrane,and sheets of the resin membranes are placed at various depths and/or onthe surface of the expansive clay mineral or the expansive clayey soil.The chemical structures from which the membrane is made is similar tothose to make ion-exchange resin particles. During manufacture,membranes may be extruded into sheets and combined with reinforcingmaterial to provide dimensional stability and mechanical strength. Useof membranes simplifies the separation of the resin from the expansiveclay mineral or the expansive clayey soil when the desired cationexchange process, e.g. replacing Na⁺ and/or Li⁺ adsorbed on the surfaceof the expansive clay minerals with K⁺, Ca²⁺, and/or Mg²⁺, is completeand when such separation of the resin from the expansive clay mineral orthe expansive clayey soil is desirable.

The swell potential of an expansive clay mineral and of an expansiveclay mineral incorporated with an amount of the swelling reduction agentcomprising at least one cementation material selected from the groupconsisting of calcite, gypsum, and potassium chloride at a first weightpercent of the amount of the swelling reduction agent and/or at leastone exchangeable cation selected from the group consisting of K⁺, Ca²⁺,and Mg²⁺ at a second weight percent of the amount of the swellingreduction agent can be simulated by the forcefield-modified molecularlevel simulation based on the water content as an initial water contentand the CEC of the expansive clay mineral and the input amounts of thecementation materials and the exchangeable cations. Theforcefield-modified molecular level simulation comprises molecularmechanics, molecular dynamics, and Monte Carlo simulation techniquespreferably with a modified Universal Forcefield shown below applied toan expansive clay mineral crystallite and an expansive clay mineral unitcell comprising a number of crystallites with periodic boundaryconditions. Compared to the forcefield-modified molecular levelsimulation for an expansive clay mineral, the forcefield-modifiedmolecular level simulation for a swelling reduction agent incorporatedexpansive clay mineral additionally simulates the interactions betweenthe expansive clay mineral particles and the non-clay swelling reductionagent particles (e.g. calcite, gypsum, and KCl) with variouscombinations of CEC, clay mineral crystallite interlayer and intra layercations, anions, and water under various fabric and structureconditions.

Modified Universal Forcefield Atom Types Atom Atomic Coor- type Atommass dination Remarks Na Na 22.99000 0 sodium Mg6 + 2 Mg 24.31000 6magnesium, octahedral, +2 oxidation state Al6 Al 26.98150 6 aluminium,octahedral Si3 Si 28.08600 3 silicon, tetrahedral K_ K 39.94800 0potassium Ca6 + 2 Ca 40.08000 6 calcium, octahedral, +2 oxidation stateDiagonal vdw Atom Lennard Radius type Jones (A) Well depth (kcal/mol) NaLJ_6_12 2.6378 0.1301E+00 Mg6 + 2 LJ_6_12 5.9090 0.9029E−06 Al6 LJ_6_124.7943 0.1329E−05 Si3 LJ_6_12 3.7064 0.1841E−05 K_ LJ_6_12 3.74230.1000E+00 Ca6 + 2 LJ_6_12 3.3990 0.2380E+00 Atom typing rules AtomHybrid- type Atom ization Formal oxidation state Mg6 + 2 Mg 0 0 0 1 Al6Al 3 0 0 1 Si3 Si 3 0 0 1

In the above modified Universal forcefield, “tetrahedral” and“octahedral” under “Atom Types” refer to the hybridization state orgeometry. “Coordination” refers to coordination number, which is thenumber of directly attached atoms. Coordination number is required forcounting the number of possible dihedrals, and is defined only for thesp2 and sp3 centers (types 2, R, and 3). Diagonal vdw refers to diagonalVan der Waals interactions represented with the conventional 12-6Lennard-Jones function that includes the short range repulsion and theattractive dispersion energy. Well depth is a parameter for theLennard-Jones (intermolecular) potential between two atoms or moleculesand is a measure of how strongly the two atoms or molecules attract eachother. “Atom typing rules” refer to the rules that define the element,hybridization, connections to other atoms, and ring membership that arecharacteristic for each atom type.

Molecular mechanics uses classical mechanics to model molecular systems.The potential energy of all systems in molecular mechanics is calculatedusing force fields. Molecular mechanics can be used to study smallmolecules as well as large biological systems or material assemblies,e.g. expansive clay minerals, with a large number of atoms. In molecularmechanics, each atom is simulated as a single particle. Each particle isassigned a radius (typically the van der Waals radius), polarizability,and a constant net charge (generally derived from quantum calculationsand/or experiment). Bonded interactions are treated as “springs” with anequilibrium distance equal to the experimental or calculated bondlength.

The potential energy of a molecular system according to molecularmechanics is calculated as a sum of individual energy termsE=E _(covalent) +E _(noncovalent)where the components of the covalent and noncovalent contributions aregiven by the following summations:E _(covalent) =E _(bond) +E _(angle) +E _(dihedral)E _(noncovalent) =E _(electrostatic) +E _(van der waals)

The exact functional form of the potential function, or force field,depends on the particular simulation program being used. Generally thebond and angle terms are modeled as harmonic potentials centered aroundequilibrium bond-length values derived from experiment or theoreticalcalculations of electronic structure performed with software which doesab-initio type calculations such as Gaussian. For accurate reproductionof vibrational spectra, the Morse potential can be used instead, atcomputational cost. The dihedral or torsional terms typically havemultiple minima and thus cannot be modeled as harmonic oscillators,though their specific functional form varies with the implementation.This class of terms may include “improper” dihedral terms, whichfunction as correction factors for out-of-plane deviations.

The non-bonded terms are much more computationally costly to calculatein full, since a typical atom is bonded to only a few of its neighbors,but interacts with every other atom in the molecule. The van der Waalsterm falls off rapidly—it is typically modeled using a “6-12Lennard-Jones potential”, which means that attractive forces fall offwith distance as r⁻⁶ and repulsive forces as r⁻¹², where r representsthe distance between two atoms. The repulsive part r⁻² is, however,unphysical, because repulsion increases exponentially. Description ofvan der Waals forces by the Lennard-Jones 6-12 potential introducesinaccuracies, which become significant at short distances. Generally acutoff radius is used to speed up the calculation so that atom pairswhose distances are greater than the cutoff have a van der Waalsinteraction energy of zero.

The electrostatic terms do not fall off rapidly with distance, andlong-range electrostatic interactions are often important features ofthe system under study. The basic functional form is the Coulombpotential, which only falls off as r⁻¹. A variety of methods are used toaddress this problem, the simplest being a cutoff radius similar to thatused for the van der Waals terms. However, this introduces a sharpdiscontinuity between atoms inside and atoms outside the radius.Switching or scaling functions that modulate the apparent electrostaticenergy are somewhat more accurate methods that multiply the calculatedenergy by a smoothly varying scaling factor from 0 to 1 at the outer andinner cutoff radii. Other more sophisticated but computationallyintensive methods are known as particle mesh Ewald (PME) and themultipole algorithm.

In addition to the functional form of each energy term, a useful energyfunction must be assigned parameters for force constants, van der Waalsmultipliers, and other constant terms. These terms, together with theequilibrium bond, angle, and dihedral values, partial charge values,atomic masses and radii, and energy function definitions, arecollectively known as a force field. Parameterization is typically donethrough agreement with experimental values and theoretical calculationsresults.

Each force field is parameterized to be internally consistent, but theparameters are generally not transferable from one force field toanother.

The primary use of molecular mechanics is in the field of moleculardynamics. This uses the force field to calculate the forces acting oneach particle and a suitable integrator to model the dynamics of theparticles and predict trajectories. Given enough sampling and subject tothe ergodic hypothesis, molecular dynamics trajectories can be used toestimate thermodynamic parameters of a system or probe kineticproperties, such as reaction rates and mechanisms.

Another application of molecular mechanics is energy minimization,whereby the force field is used as an optimization criterion. Thismethod uses an appropriate algorithm (e.g. steepest descent) to find themolecular structure of a local energy minimum. These minima correspondto stable conformers of the molecule (in the chosen force field) andmolecular motion can be modelled as vibrations around andinter-conversions between these stable conformers. It is thus common tofind local energy minimization methods combined with global energyoptimization, to find the global energy minimum (and other low energystates). At finite temperature, the molecule spends most of its time inthese low-lying states, which thus dominate the molecular properties.Global optimization can be accomplished using simulated annealing, theMetropolis algorithm and other Monte Carlo methods, or using differentdeterministic methods of discrete or continuous optimization. Whilst theforce field represents only the enthalpic component of free energy (andonly this component is included during energy minimization), it ispossible to include the entropic component through the use of additionalmethods, such as normal mode analysis.

Molecular dynamics (MD) is a computer simulation method for studying thephysical movements of atoms and molecules, and is thus a type of N-bodysimulation. The atoms and molecules are allowed to interact for a fixedperiod of time, giving a view of the dynamical evolution of the system.In the most common version, the trajectories of atoms and molecules aredetermined by numerically solving Newton's equations of motion for asystem of interacting particles, where forces between the particles andtheir potential energies are calculated using interatomic potentials ormolecular mechanics force fields. Design of a molecular dynamicssimulation should account for the available computational power.Simulation size (n=number of particles), timestep and total timeduration must be selected so that the calculation can finish within areasonable time period. However, the simulations should be long enoughto be relevant to the time scales of the natural processes beingstudied. To make statistically valid conclusions from the simulations,the time span simulated should match the kinetics of the naturalprocess.

In general terms, the Monte Carlo simulation is a technique thatapproximates solutions to quantitative problems through statisticalsampling. It is a type of simulation that explicitly and quantitativelyrepresents uncertainties. Monte Carlo simulation relies on the processof explicitly representing uncertainties by specifying inputs asprobability distributions. In order to compute the probabilitydistribution of predicted outputs (results), it is necessary topropagate (translate) the input uncertainties into uncertainties in theresults. Monte Carlo simulation is a technique for propagating theuncertainty in the various aspects of a system to the predictedperformance. In Monte Carlo simulation, the entire system is simulated alarge number of times. Each simulation is equally likely, referred to asa realization of the system. For each realization, all of the uncertainparameters are sampled (i.e., a single random value is selected from thespecified distribution describing each parameter). The system is thensimulated through time (given the particular set of input parameters)such that the performance of the system can be computed. This results ina large number of separate and independent results, each representing apossible “future” for the system (i.e., one possible path the system mayfollow through time). The results of the independent system realizationsare assembled into probability distributions of possible outcomes. As aresult, the outputs are not single values, but probabilitydistributions.

Because the forcefield-modified molecular level simulation involves alarge number of computations, the forcefield-modified molecular levelsimulation is preferably performed by a special purpose computer forcarrying out software instructions of the molecular mechanics, moleculardynamics, and Monte Carlo simulation techniques, for example, theForcite and Sorption modules of Materials Studio software.

In one embodiment, the special purpose computer is a computerillustrated in FIG. 227. In FIG. 227, the computer includes a CPU 00which performs the forcefield-modified molecular level simulationprocesses described below. The process data and instructions may bestored in memory 02. These processes and instructions may also be storedon a storage medium disk 04 such as a hard drive (HDD) or portablestorage medium or may be stored remotely. Further, the claimedadvancements are not limited by the form of the computer-readable mediaon which the instructions of the inventive process are stored. Forexample, the instructions may be stored on CDs, DVDs, in FLASH memory,RAM, ROM, PROM, EPROM, EEPROM, hard disk or any other informationprocessing device with which the computer communicates, such as a serveror computer.

Further, the claimed advancements may be provided as a utilityapplication, background daemon, or component of an operating system, orcombination thereof, executing in conjunction with CPU 00 and anoperating system such as Microsoft Windows 7, UNIX, Solaris, LINUX,Apple MAC-OS and other systems known to those skilled in the art.

The hardware elements in order to obtain the computer may be realized byvarious circuitry elements, known to those skilled in the art. Forexample, CPU 00 may be a Xenon or Core processor from Intel of Americaor an Opteron processor from AMD of America, or may be other processortypes that would be recognized by one of ordinary skill in the art.Alternatively, the CPU 00 may be implemented on an FPGA, ASIC, PLD orusing discrete logic circuits, as one of ordinary skill in the art wouldrecognize. Further, CPU 00 may be implemented as multiple processorscooperatively working in parallel to perform the instructions of theinventive forcefield-modified molecular level simulation processesdescribed below.

The computer in FIG. 227 also includes a network controller 06, such asan Intel Ethernet PRO network interface card from Intel Corporation ofAmerica, for interfacing with network 50. As can be appreciated, thenetwork 50 can be a public network, such as the Internet, or a privatenetwork such as an LAN or WAN network, or any combination thereof andcan also include PSTN or ISDN sub-networks. The network 50 can also bewired, such as an Ethernet network, or can be wireless such as acellular network including EDGE, 3G and 4G wireless cellular systems.The wireless network can also be WiFi, Bluetooth, or any other wirelessform of communication that is known.

The computer further includes a display controller 08, such as a NVIDIAGeForce GTX or Quadro graphics adaptor from NVIDIA Corporation ofAmerica for interfacing with display 10, such as a Hewlett PackardHPL2445w LCD monitor. A general purpose I/O interface 12 interfaces witha keyboard and/or mouse 14 as well as a touch screen panel 16 on orseparate from display 10. General purpose I/O interface also connects toa variety of peripherals 18 including printers and scanners, such as anOfficeJet or DeskJet from Hewlett Packard.

A sound controller 20 is also provided in the computer, such as SoundBlaster X-Fi Titanium from Creative, to interface withspeakers/microphone 22 thereby providing sounds and/or music.

The general purpose storage controller 24 connects the storage mediumdisk 04 with communication bus 26, which may be an ISA, EISA, VESA, PCI,or similar, for interconnecting all of the components of the computer. Adescription of the general features and functionality of the display 10,keyboard and/or mouse 14, as well as the display controller 08, storagecontroller 24, network controller 06, sound controller 20, and generalpurpose I/O interface 12 is omitted herein for brevity as these featuresare known.

In a preferred embodiment, the special purpose computer is a supercomputer with a high-level computational capacity performing up toquadrillions of FLOPS (floating-point operations per second).

The forcefleld-modified molecular level simulation for an expansive claymineral or a swelling reduction agent incorporated expansive claymineral based on the water content and CEC of the expansive clay mineralmay comprise multiple steps, e.g. replacing 0-100% of a total number ofat least one non-K⁺, Ca²⁺, and Mg²⁺ exchangeable cation withexchangeable Ca²⁺, and/or Mg²⁺ cations in a crystallite of the expansiveclay mineral, sorption of water molecules onto individual crystallitesof the expansive clay mineral, assemblage of crystallites of theexpansive clay mineral to form unit cells through natural randomnessconcepts, compaction of unit cells to the maximum density, relaxation ofunit cells to simulate stress relief, and finally volume change uponsorption of water molecules in the pore spaces of unit cells.

In one embodiment, the expansive clay mineral for theforcefield-modified molecular level simulation comprises a single typeof expansive clay mineral. In another embodiment, the expansive claymineral for the forcefield-modified molecular level simulation comprisestwo or more types of expansive clay minerals. In this case, theforcefield-modified molecular level simulation may be performedseparately with each individual type of expansive clay mineral, and theswell potential of the mixed expansive clay mineral may be obtained bycombining the forcefield-modified molecular level simulation resultsfrom the individual types of expansive clay minerals according to theirweight proportions or weight percentages in the mixed expansive claymineral. When the swelling reduction agent is incorporated into theexpansive clay mineral comprising two or more types of expansive clayminerals, the swelling reduction agent may be considered to bedistributed among different types of expansive clay minerals in amountsproportional to the weight percentages of the different types of theexpansive clay minerals. The weight percentages of the different typesof the expansive clay minerals relative to the total weight of the(mixed) expansive clay mineral can be determined by a mineralogicalanalysis using, for example, powder X-ray diffraction (XRD), scanningelectron microscopy (SEM) with associated energy dispersive microanalysis (EDA), optical microscopy and petrographic analysis. In someembodiments, the expansive clay mineral for the forcefield-modifiedmolecular level simulation is at least one selected from the groupconsisting of smectite, bentonite, montmorillonite, beidellite,vermiculite, attapulgite, nontronite, illite, and chlorite. In apreferred embodiment, the expansive clay mineral comprises at least oneof smectite, bentonite, montmorillonite.

For illustration of the forcefield-modified molecular level simulation,in a simplistic example, the forcefield-modified molecular levelsimulation is used to simulate water sorption and swelling of anexpansive clay mineral, preferably a montmorillonite expansive claymineral, without the swelling reduction agent and with Na⁺ as the soleexchangeable cation (e.g. Na-montmorillonite). The forcefield-modifiedmolecular level simulation starts with a molecular level simulation ofsorption of water molecules onto a single (montmorillonite) crystalliteto form a water sorbed (montmorillonite) crystallite of the expansiveclay mineral with the initial water content. It represents the processesof water mixing with the clay in the laboratory conditions or theinteraction of clay particles with water during the geologicaldepositional processes. In some embodiments, the crystallite size of the(montmorillonite) expansive clay mineral may be in the range of 10-120Å, 30-110 Å, or 59-108 Å. In other embodiments, the (montmorillonite)crystallite size of the expansive clay mineral may be(13-52)×(27-108)×(10-40) Å, (20-40)×(40-90)×(15-30) Å, preferably(25-35)×(50-70)×(15-25) Å, or more preferably 26×54×20 Å.

In one embodiment, the sorption of water molecules onto the single(montmorillonite) crystallite is simulated using Sorption and Forcitemodules of Materials Studio software. Sorption module is based on MonteCarlo simulation technique in which water molecules get sorbed on theclay mineral particle on its surfaces, interlayer, and edges. InSorption module, sorbate (single water molecules) is absorbed in thesorbent framework of clay mineral molecule. Fixed loading may be used tofind the global minimum energy sites for the water molecules in a claymineral crystallite by running cycles of fixed loading simulation serieswhere the temperature is steadily reduced over the series. MetropolisMonte Carlo method used in the Sorption module is a Monte Carlo methodin which trial configurations are generated without bias (SeeMetropolis, N.; Rosenbluth, A. W.; Rosenbluth, M. N.; Teller, A. H.;Teller, E. J. (1953), “cccc” Chem. Phys., 21, 1087, incorported hereinby reference in its entirety). This method is preferably selected forthe simulations as it treats the sorbate structure as rigid and onlyrigid body translations and reorientations are incorporated. In theSorption module, ratios for exchange, conformer, rotate, translate, andregrow are preferably selected as 0.39, 0.2, 0.2, 0.2, 0.2,respectively, while the corresponding probabilities are preferably 0.39,0.2, 0.2, 0.2, and 0.2. Amplitudes adopted for rotation and translationare preferably 5° and 1 Å, respectively.

In some embodiments, the molecular level simulation of water sorptiononto the single crystallite of the expansive clay mineral comprisesmultiple phases to satisfy the crystalline swelling, e.g. a phase ofwater molecules occupying the locations next to cations (e.g. Na⁺)present in the interlayer of the crystallite to hydrate the cations, aphase of water molecules bonding with the edges of the crystallite, aphase of water molecules bonding with the ends of the crystallite, and aphase of water molecules bonding with the interlayer of the crystallite,and comprises 25,000 Monte Carlo simulation steps at each phase. Afterthe completion of the Monte Carlo simulation steps at each phase of thewater sorption, equilibration is achieved in 10,000-20,000 steps, orpreferably 12,000-18,000 steps, or more preferably 15,000 steps to atemperature preferably at 298° K. In a preferred embodiment, theforcefield shown above is used for the sorption and molecular dynamicssimulations on an expansive clay mineral. Ewald summation method ispreferably adopted for the electrostatic forces, while atom basedsummation is preferably used for van der Waals forces with cubic splinecut off at 12.5 Å.

Also after the completion of the Monte Carlo simulation steps at eachphase of the water sorption, the water sorbed crystallite of theexpansive clay mineral is preferably stabilized through molecularmechanics and dynamics simulation. In one embodiment, a Forcite moduleof the Materials Studio software is used for the purpose. In Forcite,NPT (constant number of particles, pressure, and temperature) ensembleis preferably used and simulations are preferably performed using theforcefield shown above for a period of 5 to 30 ps in 0.5 fs intervals oruntil a constant volume is achieved. Berendsen thermostat with a decayconstant of 0.1 ps is preferably used to control the temperature duringthe simulation. During the molecular dynamics simulation, temperaturemay be kept constant at 298° K. Simulations are preferably carried outat about atmospheric pressure (e.g. 100 kPa) and Berendsen barostat withdecay constant of 0.1 ps is preferably used to control the pressure ofthe system.

The molecular level simulation of water sorption onto each individualcrystallite of the expansive clay mineral results in water moleculessorbed on the surface, edges, and the interlayer of the crystallite. Thewater sorbed in the interlayer causes a lattice expansion or an increasein lattice d-spacing in crystal lattice of the expansive clay mineral.In some embodiments, the maximum lattice expansion of the expansive claymineral is about 17.5 Å, or three layers of interlayer water equivalentto about 30% (w/w) in water content accommodated in the interlayer spaceof the crystallite of the expansive clay mineral. Any further increasein water content takes place at the edges and ends of the crystallite ofthe expansive clay mineral.

Next, the forcefield-modified molecular level simulation performs aMonte Carlo simulation of a natural randomness process of assemblingwater sorbed crystallites of the expansive clay mineral into loose cubicunit cells, with each loose cubic unit cell containing N water sorbedcrystallites, wherein N is in the range of 2-8, preferably 3-6, or morepreferably 4, and each loose cubic unit cell has a size of 125×125×125Å. In the cubic space of the loose cubic unit cell, the N water sorbedcrystallites are mixed together in loose form, occupying separate randompositions without overlapping with one another. In some embodiments, theN crystallites in the loose cubic unit cell may take the followingrelative positions to one another: parallel to faces, edge to edge, edgeto face, or an intermediate form depending on the charge distribution oneach crystallite and the water content of the crystallites. In oneembodiment, the loose cubic unit cells may repeat infinitely in spacewith the superposition of the periodic boundary conditions to createexpansive clay fabrics during the loose mix state, for example, usingthe Sorption module of the Materials Studio software.

Further, the forcefield-modified molecular level simulation performs amolecular level simulation of compressing the loose cubic unit cell at afirst confining pressure to form a compacted unit cell of a desireddensity to simulate the fabric and structure in a compacted expansiveclay mineral. In a preferred embodiment, this part of theforcefield-modified molecular level simulation is performed using theForcite molecular dynamics module of the Materials Studio software.Preferably, an NPT ensemble is used to compress the loose cubic unitcell to a high density, for example, a dry density of 1.2-2.5 g/cm³, ata first confining pressure of, for example, 0.01-1 GPa, which simulatesdifferent levels of geological and laboratory compaction pressures toresult in different maximum densities of the compacted unit cell. Forexample, a first confining pressure of an order of 1 GPa causes quickcompaction and may be closely representative of dynamic and static quicktype of compaction using the laboratory and field equipment. On theother hand, a reduced first confining pressure of an order of 0.01 to0.1 GPa can result in slow compaction and hence may be simulating moreclosely slow compaction/consolidation pressures for the geologicaldeposits. In one embodiment, the simulation is run to at least 10 ps, orat least 30 ps at an interval of 0.1 fs, to achieve the maximum density.In a preferred embodiment, Berendsen thermostat and Parrinello barostatare used. As Berendsen barostat applies pressure in all the directionsin a way to keep the unit cell dimensions equal, the correspondingreduction of volume on all the faces of the periodic boundary cellremains uniform. Therefore, Berendsen barostat does not simulate thereal compaction process in which stresses vary along the faces under auniform compaction pressure process. On the other hand, using Parrinellobarostat can result in a more realistic way of compaction by varying thestresses on the faces depending on the shear stresses generated in theunit cell. The resulting fabric is also more random and face to edgefabric on lower moisture content while more oriented and parallel fabricis created on higher moisture contents. The dynamics compactionsimulation is continued until a maximum density is achieved.

Since expansive clay deposits present at shallow subsurface level haveexperienced a stress relief due to removal of high geological pressuresinitially responsible for the creation of highly compacted soilstructure, still further next, the forcefield-modified molecular levelsimulation may preferably perform a molecular level simulation ofrelaxing the compacted unit cell at a second confining pressure that isless than the first confining pressure to form a stress relaxed unitcell to simulate the overconsolidation process by the removal ofgeological overburden. In some embodiments, the lower second confiningpressure is in the range of 500-2000 kPa, or 800-1500 kPa, or 1000 kPa.As a result of stress relief simulation, the stress relaxed unit cellachieves a lesser density due to more void space and an increase in thelattice d-spacing of the crystallite. In a preferred embodiment, thispart of the forcefield-modified molecular level simulation is performedusing the Forcite molecular dynamics and the Parrinello barostat of theMaterials Studio software.

Lastly, the forcefield-modified molecular level simulation performs amolecular level simulation of water sorption onto and swelling of thecompacted unit cell at the first confining pressure or the stressrelaxed unit cell at the second confining pressure to simulate the watersorption in the pores of the unit cell and swelling/volume change of theexpansive clay mineral to form a swollen compacted unit cell or aswollen stress relaxed unit cell comprising the N water sorbedcrystallites of the expansive clay mineral. In this part of theforcefield-modified molecular level simulation, the compacted unit cellor the stress relaxed unit cell is sorbed with water molecules in theintra and interlayer of the crystallites, at multiple phases similar tothose for the water sorption onto a single crystallite described above,with 25,000 Monte Carlo simulation steps for each phase of the watersorption. Each Monte Carlo simulation step for the water sorptionresults in an increase in water content of the swollen compacted unitcell or the swollen stress relaxed unit cell. Upon the completion ofeach water sorption phase, the swollen compacted unit cell or theswollen stress relaxed unit cell is dynamically stabilized, preferablyby using the Forcite module of the Materials Studio software. Thestabilization by molecular dynamics causes the movement of molecules tostable positions and result in a stable expanded structure under thefirst confining pressure for the compacted unit cell or the secondconfining pressure for the stress relaxed unit cell. The process ofwater molecules sorption and the subsequent stabilization by moleculardynamics is repeated until a stabilized volume/density is obtained, or aswell cutoff point is reached. The extent of the swelling of the swollencompacted unit cell or the swollen stress relaxed unit cell comprisingthe N water sorbed crystallites of the expansive clay mineral at theswell cutoff point corresponds to the swell potential of the expansiveclay mineral, and the water content of the swollen compacted unit cellor the swollen stress relaxed unit cell comprising the N water sorbedcrystallites of the expansive clay mineral at the swell cutoff pointcorresponds to the final water content (FWC) of the expansive claymineral. In one embodiment, the swell cutoff point is reached when aMonte Carlo simulation step for the water sorption onto the compactedunit cell at the first confining pressure or the stress relaxed unitcell at the second confining pressure results in an increase of about1-5% (w/w), or preferably about 2-4% (w/w) in the water content of theswollen compacted unit cell or the swollen stress relaxed unit cell. Inanother embodiment, this part of the forcefield-modified molecular levelsimulation further comprises determining a dry density of the swollenstress relaxed unit cell comprising the N water sorbed crystallites ofthe expansive clay mineral, and the swell cutoff point is reached whenthe dry density of the swollen stress relaxed unit cell comprising the Nwater sorbed crystallites of the expansive clay mineral is in the rangeof 0.1-0.8 g/cm³, 0.2-0.6 g/cm³, or 0.3-0.5 g/cm³. In still anotherembodiment, this part of the forcefield-modified molecular levelsimulation further comprises determining a total cohesive energy density(TCED) of the swollen stress relaxed unit cell comprising the N watersorbed crystallites of the expansive clay mineral during the dynamicssimulation process, and the swell cutoff point is reached when the TCEDof the swollen stress relaxed unit cell comprising the N water sorbedcrystallites of the expansive clay mineral is in the range of1×10⁸-8×10⁸ J/m³, 3×10⁸-6×10⁸ J/m³, or 4×10⁸-5×10⁸ J/m³. In a preferredembodiment, the total cohesive energy density is determined using theForcite module of the Materials Studio software. In one embodiment, theswelling or expansion of the compacted or stress relaxed unit celloccurs both in the interlayer and intracrystallite space. In anotherembodiment, the maximum swelling occurs in the intracrystallite spacewhile the interlayer space expands to a maximum value of 17.5 Åaccommodating three interlayer water layers equivalent to 30% (w/w) inwater content.

According to the present disclosure, cohesive energy density (CED) is anexcellent indicator of the interaction of the soil structure with thewater sorption and the consequent volume change. Cohesive energy densityis the amount of energy needed to completely remove unit volume ofmolecules from their neighbors to infinite separation (an ideal gas).CED is highly sensitive to various volume change variables such as watercontent, density, CEC, type and percentage of exchangeable andnon-exchangeable cations, and anions. Total CED of any combination ofmolecules is contributed from two components, i.e., electrostatic andvan der Waals forces. Contribution from van der Waals could either berepulsion or attraction in nature, while it is always attraction innature from electrostatic forces. A general trend is that low CECexpansive clay mineral crystallites produce lesser CED, while a higherCEC and the expansive clay mineral crystallites sorbed with othercompounds (e.g. cementation materials, such as calcite, gypsum, and KCl)show higher values of CED. Total CED has been found to be increasingwith an increase in CEC, density, cementation, and bivalent cations anddecreasing with water content, while van der Waals CED reduces andbecomes repulsion in nature with the same variation of the aboveparameters. For the same CEC, lesser water content results in highercohesive energy, but for same density/moisture, higher CEC crystallitesachieve much higher cohesive energy. As cohesion in clay mineralparticles is a result of the hydrogen bonding between their surfaces andthe water, more number of charge deficiency centers in higher CEC clayminerals results in more number of hydrogen bonds and consequentlyraising the electrostatic attraction CED. However, at the same time, vander Waals repulsions increase due to the high vicinity of thecrystallites. Therefore, higher total cohesive energy mixes havecorresponding higher repulsion van der Waals. These additional repulsionforces play an important role in the expansion/swell behavior of theclay mineral particles in addition to the hydration by water molecules.Similarly, interaction with gypsum and calcite also causes an increasein cohesive energy density due to the extra bonding created by thecations and anions. Although there is an increase in repulsion due tovan der Waals forces, increase in attraction forces due to electrostaticcomponent has much higher value and far outweighs the repulsion forcesin these cases.

Compared with the forcefield-modified molecular level simulation for anexpansive clay mineral without the swelling reduction agent and with Na⁺as the sole exchangeable cation described above, the forcefield-modifiedmolecular level simulation for an expansive clay mineral incorporatedwith one or more cementation materials, such as gypsum, calcite, andKCl, as the swelling reduction agent further comprises a molecular levelsimulation of sorption of the cementation materials, e.g. gypsum (i.e.Ca²⁺ and SO₄ ²⁻), KCl (i.e. K⁺ and Cl⁻, and/or calcite (i.e. Ca²⁺ andCO₃ ²⁻) in amounts proportional to their weight percentages in theswelling reduction agent onto the water sorbed crystallite of theexpansive clay mineral with the initial water content, e.g. in andaround the crystallite, on the surface and the interlayer of thecrystallite, following the molecular level simulation of water sorptiononto the crystallite of the expansive clay mineral. In some embodiments,cations of relatively small sizes such as Ca²⁺ enters the interlayerwhile bigger anions such as SO₄ ²⁻, Cl⁻ and CO₃ ²⁻ envelop the surfaceof the crystallite of the expansive clay mineral. These cementationmaterials provide additional binding or cohesive forces to theindividual and group of clay mineral particles. In a preferredembodiment, this part of the forcefield-modified molecular levelsimulation is performed using the Sorption module of the MaterialsStudio software. The rest of the forcefield-modified molecular levelsimulation procedure, including the molecular level simulation ofassembling a plurality of the water sorbed crystallites to form a loosecubic unit cell of the expansive clay mineral comprising the cementationmaterials as the swelling reduction agent, the molecular levelsimulation of compressing the loose cubic unit cell at a first,relatively high confining pressure to form a compacted unit cell of theexpansive clay mineral comprising the cementation materials as theswelling reduction agent (i.e. compaction), the molecular levelsimulation of relaxing the compacted unit cell at a second, relativelylow confining pressure to form a stress relaxed unit cell of theexpansive clay mineral comprising the cementation materials as theswelling reduction agent (i.e. stress relief), and the molecular levelsimulation of water sorption onto and swelling of the compacted unitcell at the first confining pressure or the stress relaxed unit cell atthe second confining pressure to form a swollen compacted unit cell or aswollen stress relaxed unit cell of the expansive clay mineralcomprising the cementation materials as the swelling reduction agent issimilar to that for the expansive clay mineral without the swellingreduction agent and with Na⁺ as the sole exchangeable cation describedabove. In one embodiment, the swell cutoff point for the molecular levelsimulation of water sorption onto and swelling of the compacted unitcell at the first confining pressure or the stress relaxed unit cell atthe second confining pressure to form the swollen compacted unit cell orthe swollen stress relaxed unit cell of the expansive clay mineralcomprising the cementation materials as the swelling reduction agent isreached when a Monte Carlo simulation step for the water sorptionresults in an increase of about 1-5% (w/w), or preferably about 2-4%(w/w) in the water content of the swollen compacted unit cell or theswollen stress relaxed unit cell of the expansive clay mineralcomprising the cementation materials as the swelling reduction agent. Inanother embodiment, the forcefield-modified molecular level simulationfor the expansive clay mineral incorporated with one or more cementationmaterials of gypsum, calcite, and KCl as the swelling reduction agentfurther comprises determining a first total CED (TCED1) of the stressrelaxed unit cell of the expansive clay mineral comprising thecementation materials as the swelling reduction agent, determining asecond TCED (TCED2) of the stress relaxed unit cell of the expansiveclay mineral without the cementation materials and with Na⁺ as the soleexchangeable cation, determining the difference (ΔTCED) between TCED1and TCED2, i.e. ΔTCED=TCED1−TCED2, determining a third total CED (TCED3)of the swollen stress relaxed unit cell of the expansive clay mineralcomprising the cementation materials as the swelling reduction agentduring the molecular level simulation of water sorption onto andswelling of the stress relaxed unit cell of the expansive clay mineralcomprising the cementation materials as the swelling reduction agent atthe second confining pressure to form the swollen stress relaxed unitcell of the expansive clay mineral comprising the cementation materialsas the swelling reduction agent, and comparing TCED3 with the sum ofΔTCED and a fourth TCED (TCED4), i.e. ΔTCED+TCED4, wherein TCED4 is theTCED of the swollen stress relaxed unit cell of the expansive claymineral without the cementation materials and with Na⁺ as the soleexchangeable cation at the swell cutoff point and is in the range of1×10⁸-8×10⁸ J/m³, 3×10⁸-6×10⁸ J/m³, or 4×10⁸-5×10⁸ J/m³. When TCED3equals ΔTCED TCED4, the swell cutoff point for the molecular levelsimulation of water sorption onto and swelling of the stress relaxedunit cell of the expansive clay mineral comprising the cementationmaterials as the swelling reduction agent at the second confiningpressure to form the swollen stress relaxed unit cell of the expansiveclay mineral comprising the cementation materials as the swellingreduction agent is reached. In this embodiment, all of the TCEDs arepreferably determined by using the Forcite dynamics module of theMaterials Studio software.

Compared with the forcefield-modified molecular level simulation for anexpansive clay mineral without the swelling reduction agent and with Na⁺as the sole exchangeable cation described above, the forcefield-modifiedmolecular level simulation for an expansive clay mineral incorporatedwith one or more exchangeable K⁺, Ca²⁺, and/or Mg²⁺ as the swellingreduction agent further comprises a molecular level simulation ofreplacing 0-100% of the total number of the exchangeable Na⁺ with theinput amount of exchangeable K⁺, Ca²⁺, and/or Mg²⁺ cations in acrystallite of the expansive clay mineral prior to the molecular levelsimulation of water sorption onto the crystallite of the expansive claymineral comprising the exchangeable K⁺, Ca²⁺, and/or Mg²⁺ cations toform a water sorbed crystallite of the expansive clay mineral comprisingthe exchangeable K⁺, Ca²⁺, and/or Mg²⁺ cations with the initial watercontent. However, besides Na⁺, other non-K⁺, Mg²⁺, and Ca²⁺ exchangeablecations, such as Li⁺, may be similarly replaced in the simulation. Thegeneral behavior of water molecules sorption is the same for acrystallite with multiple exchangeable cations. However, some angularshift of the crystallite in space may occur in case of multiple cations.This phenomenon may be due to the presence of exchangeable cations ofdifferent charges, sizes, and hydration radii and positioned at randomlocations in the interlayer. These cations while getting hydrated maygenerate different level of forces in the crystallite interlayer spaceand consequently cause an angular shift in the crystallite position inspace. The rest of the forcefield-modified molecular level simulationprocedure, including the molecular level simulation of assembling aplurality of the water sorbed crystallites to form a loose cubic unitcell of the expansive clay mineral comprising the exchangeable K⁺, Ca²⁺,and/or Mg²⁺ cations as the swelling reduction agent, the molecular levelsimulation of compressing the loose cubic unit cell at a first confiningpressure to form a compacted unit cell of the expansive clay mineralcomprising the exchangeable K⁺, Ca²⁺, and/or Mg²⁺ cations as theswelling reduction agent (i.e. compaction), the molecular levelsimulation of relaxing the compacted unit cell at a second confiningpressure to form a stress relaxed unit cell of the expansive claymineral comprising the exchangeable K⁺, Ca²⁺, and/or Mg²⁺ cations as theswelling reduction agent (i.e. stress relief), and the molecular levelsimulation of water sorption onto and swelling of the compacted unitcell at the first confining pressure or the stress relaxed unit cell atthe second confining pressure to form a swollen compacted unit cell or aswollen stress relaxed unit cell of the expansive clay mineralcomprising the exchangeable K⁺, Ca²⁺, and/or Mg⁺ cations as the swellingreduction agent is similar to that for the expansive clay mineralwithout the swelling reduction agent and with Na⁺ as the soleexchangeable cation described above. In one embodiment, the swell cutoffpoint for the molecular level simulation of water sorption onto andswelling of the compacted unit cell at the first confining pressure orthe stress relaxed unit cell at the second confining pressure to form aswollen compacted unit cell or a swollen stress relaxed unit cell of theexpansive clay mineral comprising the exchangeable K⁺, Ca²⁺, and/or Mg²⁺cations as the swelling reduction agent is reached when a Monte Carlosimulation step for the water sorption results in an increase of about1-5% (w/w), or preferably about 2-4% (w/w) in the water content of theswollen compacted unit cell or the swollen stress relaxed unit cell ofthe expansive clay mineral comprising the exchangeable K⁺, Ca²⁺, and/orMg²⁺ cations as the swelling, reduction agent. In another embodiment,the forcefield-modified molecular level simulation for the expansiveclay mineral comprising the exchangeable K⁺, Ca²⁺, and/or Mg²⁺ cationsas the swelling reduction agent further comprises determining a firsttotal CED (TCED1) of the stress relaxed unit cell of the expansive claymineral comprising the exchangeable K⁺, Ca²⁺, and/or Mg²⁺ cations as theswelling reduction agent, determining a second TCED (TCED2) of thestress relaxed unit cell of the expansive clay mineral without thecementation materials (e.g. calcite, gypsum, and KCl) and with Na⁺ asthe sole exchangeable cation (i.e. without exchangeable K⁺, Ca²⁺, and/orMg²⁺ cations as the swelling reduction agent), determining thedifference (ΔTCED) between TCED1 and TCED2, i.e. ΔTCED=TCED1−TCED2,determining a third total CED (TCED3) of the swollen stress relaxed unitcell of the expansive clay mineral comprising the exchangeable K⁺, Ca²⁺,and/or Mg²⁺ cations as the swelling reduction agent during the molecularlevel simulation of water sorption onto and swelling of the stressrelaxed unit cell comprising the exchangeable K⁺, Ca²⁺, and/or Mg²⁺cations as the swelling reduction agent at the second confining pressureto form the swollen stress relaxed unit cell comprising the exchangeableK⁺, Ca²⁺, and/or Mg²⁺ cations as the swelling reduction agent, andcomparing TCED3 with the sum of ΔTCED and a fourth TCED (TCED4), i.e.ΔTCED+TCED4, wherein TCED4 is the TCED of the swollen stress relaxedunit cell of the expansive clay mineral without the cementationmaterials and with Na⁴ as the sole exchangeable cation at the swellcutoff point and is in the range of 1×10⁸-8×10⁸ J/m³, 3×10⁸-6×10⁸ J/m³,or 4×10⁸-5×10⁸ J/m³. When TCED3 equals ΔTCED+TCED4, the swell cutoffpoint for the molecular level simulation of water sorption onto andswelling of the stress relaxed unit cell at the second confiningpressure to form the swollen stress relaxed unit cell of the expansiveclay mineral comprising the exchangeable K⁺, Ca²⁺, and/or Mg²⁺ cationsas the swelling reduction agent is reached. In this embodiment, all ofthe TCEDs are preferably determined by using the Forcite dynamics moduleof the Materials Studio software.

When the swelling reduction agent comprises at least one of thecementation materials, i.e. calcite, gypsum, and KCl, as well as atleast one of exchangeable K⁺, exchangeable Ca²⁺, and/or exchangeableMg²⁺, compared to the forcefield-modified molecular level simulation foran expansive clay mineral without the swelling reduction agent and withNa⁺ as the sole exchangeable cation, the forcefield-modified molecularlevel simulation further comprises a molecular level simulation ofreplacing 0-100% of a total number of non-K⁺, Ca²⁺, and Mg²⁺exchangeable cations (i.e. Na⁺ in this case) with the input amount ofexchangeable K⁺, Ca²⁺, and/or Mg²⁺ cations in a crystallite of theexpansive clay mineral prior to the molecular level simulation of watersorption onto the crystallite of the expansive clay mineral comprisingthe exchangeable K⁺, Ca²⁺, and/or Mg²⁺ cations to form a water sorbedcrystallite of the expansive clay mineral comprising the exchangeableK⁺, Ca²⁺, and/or Mg²⁺ cations with the initial water content, and amolecular level simulation of sorption of the cementation materials,e.g. gypsum (i.e. Ca²⁺ and SO₄ ²⁻), KCl (i.e. K⁺ and Cl⁻), and/orcalcite (i.e. Ca²⁺ and CO₃ ²⁻) in amounts proportional to their weightpercentages in the swelling reduction agent onto the water sorbedcrystallite of the expansive clay mineral comprising the exchangeableK⁺, Ca²⁺, and/or Mg²⁺ cations with the initial water content, e.g. inand around the crystallite, on the surface and the interlayer of thecrystallite. The rest of the forcefield-modified molecular levelsimulation can be carried out in the same fashion as that for theexpansive clay mineral comprising either the cementation materials orthe exchangeable K⁺, Ca²⁺, and/or Mg²⁺ cations as the swelling reductionagent described above.

Thus, the swell potential of the swelling reduction agent-incorporatedexpansive clay mineral S_(i(ECM)) can be determined by theforcefield-modified molecular level simulation if the type(s) and theamount(s) of the swelling reduction agent(s) are known. Conversely, if atarget swell potential of the swelling reduction agent-incorporatedexpansive clay mineral is set based on the pre-set level T, the type(s)and the amount(s) of the swelling reduction agent(s) that need to beincorporated into the expansive clay mineral to obtain the target swellpotential can be determined by the forcefield-modified molecular levelsimulation based on the water content (as the initial water content,IWC) and the CEC of the expansive clay mineral.

The pre-set level T, in one embodiment, may be set based on anacceptable level of swell potential of the expansive clay mineral, forexample, a level at which the expansive clay mineral may not exertenough force on a building or other structure built on or within theexpansive clay mineral to cause damage, such as 5-10%, 6-9%, or 7-8%. Insome embodiments, the building or other structure built on or within theexpansive clay mineral includes, without limitation, a buildingfoundation, a railway line foundation, a pipe, a footing, a landfillliner, a nuclear waste storage containment liner, a swimming pool, awall, a driveway, a road, a pavement, a basement floor, and a wellbore.If these structures are built on or within the expansive clay mineral orexpansive clayey soil comprising the expansive clay mineral with anunacceptably high swell potential, particularly in regions with verydefined wet and dry periods, the swelling of the expansive clay mineralor the expansive clayey soil when the expansive clay mineral or theexpansive clayey soil is wet can cause the structures to heave or lift,and the shrinking of the expansive clay mineral or the expansive clayeysoil when the expansive clay mineral or the expansive clayey soilbecomes dry can cause uneven settling of sediment underneath thestructures, resulting in damages to or even failures of the structures,such as large cracks in walls, foundations and swimming pool shells,buckling of driveway and roads, jamming of doors and windows, breakageof water or sewage pipes, and destabilization and even collapsing of awellbore.

In some embodiments, there may be various potential ways of using eithera single swelling reduction agent or combinations of the swellingreduction agents to obtain a swell potential of the swelling reductionagent incorporated expansive clay mineral S_(i(ECM)) that is no greaterthan the pre-set level T according to the forcefield-modified molecularlevel simulation. In those cases, the preferred choices for the singleswelling reduction agent or the combinations of the swelling reductionagents to be incorporated into the expansive clay mineral are thosewhere the amount of calcite needed as determined according to theforcefield-modified molecular level simulation is in the range of10-70%, 20-60%, or 30-50% of the total weight of the swelling reductionagent incorporated expansive clay mineral, the amount of gypsum neededas determined according to the forcefield-modified molecular levelsimulation is in the range of 5-75%, 10-60%, 15-50%, or 20-40% of thetotal weight of the swelling reduction agent incorporated expansive claymineral, the amount of KCl needed as determined according to theforcefield-modified molecular level simulation is in the range of 2-30%,5-25%, or 10-20% of the total weight of the swelling reduction agentincorporated expansive clay mineral, and/or the amount of theexchangeable K⁺, Ca²⁺, and/or Mg²⁺ needed as determined according to theforcefield-modified molecular level simulation replaces 5-100%, 10-90%,20-80%, 30-70%, or 40-60% of the total number of non-K⁺, Ca²⁺, or Mg²⁺exchangeable cation(s), such as Na⁺ and Li⁺, previously adsorbed on thesurface of the expansive clay mineral.

In some embodiments, the expansive clay mineral comprises Na⁺ as theonly exchangeable cation and replacing 40-80%, 50-70%, or 60% of thetotal number of Na⁺ with K⁺ in the expansive clay mineral results in a8-25%, 10-20%, or 15% reduction in the swell potential of the expansiveclay mineral, depending on the type of the expansive clay mineral, andthe CEC and the initial water content of the expansive clay mineral,according to the forcefield-modified molecular level simulation.

In other embodiments, the expansive clay mineral comprises Na⁺ as theonly exchangeable cation and replacing 40-80%, 50-70%, or 60% of thetotal number of Na⁺ with Ca²⁺ in the expansive clay mineral results in a20-70%, 30-65%, or 40-55% reduction in the swell potential of theexpansive clay mineral, depending on the type of the expansive claymineral, and the CEC and the initial water content of the expansive claymineral, according to the forcefield-modified molecular levelsimulation.

In still other embodiments, the expansive clay mineral comprises Na⁺ asthe only exchangeable cation and replacing 40-80%, 50-70%, or 60% of thetotal number of Na⁺ with Mg²⁺ in the expansive clay mineral results in a30-60%, or 40-50% reduction in the swell potential of the expansive claymineral, depending on the type of the expansive clay mineral, and theCEC and the initial water content of the expansive clay mineral,according to the forcefield-modified molecular level simulation.Compared with K⁺, bivalent cations such as Ca²⁺ and Mg²⁺ can result inextra binding to the crystallite layers and hence cause a greaterreduction in swell potential according to the forcefield-modifiedmolecular level simulation.

In some embodiments, incorporating gypsum into an expansive clay mineralat 10-40%, or 15-30%, or 20-25% of the total weight of the incorporatedexpansive clay mineral reduces the swell potential of the expansive claymineral at least 70%, at least 80%, or at least 90% depending on thetype of the expansive clay mineral, and the CEC and the initial watercontent of the expansive clay mineral, according to theforcefield-modified molecular level simulation.

In other embodiments, incorporating calcite into an expansive claymineral at 3-30%, 5-25%, 8-20%, or 10-15% of the total weight of theincorporated expansive clay mineral reduces the swell potential of theexpansive clay mineral at least 75%, at least 80%, or at least 90%depending on the type of the expansive clay mineral, and the CEC and theinitial water content of the expansive clay mineral, according to theforcefield-modified molecular level simulation.

In still other embodiments, incorporating KCl into an expansive claymineral at 3-30%, 5-25%, 8-20%, or 10-15% of the total weight of theincorporated expansive clay mineral reduces the swell potential of theexpansive clay mineral at least 80%, at least 85%, or at least 90%,depending on the type of the expansive clay mineral, and the CEC and theinitial water content of the expansive clay mineral, according to theforcefield-modified molecular level simulation.

According to a second aspect, the present disclosure relates to anothermethod of reducing the swell potential of an expansive clay mineralhaving a first water content and a cation exchange capacity (CEC). Themethod includes (a) carrying out a forcefield-modified molecular levelsimulation to determine a second water content of a wetted expansiveclay mineral to be formed by wetting the expansive clay mineral withwater, wherein the forcefield-modified molecular level simulationcomprises molecular mechanics, molecular dynamics, and Monte Carlosimulation techniques configured to simulate a reduced swell potentialS_(w) of the wetted expansive clay mineral that is no greater than apre-set level T based on the cation exchange capacity (CEC) of theexpansive clay mineral and the second water content of the wettedexpansive clay mineral as an initial water content (IWC), wherein thesecond water content as the initial water content (IWC) is greater thanthe first water content but no greater than a final water content (FWC)of the expansive clay mineral when the expansive clay mineral reachesthe swell potential, and (b) wetting the expansive clay mineral withwater to form the wetted expansive clay mineral having the second watercontent and the reduced swell potential S_(w).

In one embodiment, the expansive clay mineral does not containcementation materials, such as calcite, gypsum, and KCl, and comprisesNa⁺ as the only exchangeable cation. In this embodiment, theforcefield-modified molecular level simulation is the same as theforcefield-modified molecular level simulation for the expansive claymineral without the swelling reduction agent and with Na⁺ as the soleexchangeable cation described in the first aspect, except that theinitial water content used during the molecular level simulation ofwater sorption onto the crystallite of the expansive clay mineral toform a water sorbed crystallite with the initial water content is thesecond water content of the wetted expansive clay mineral. The secondwater content is greater than the first water content but no greaterthan a final water content (FWC) of the expansive clay mineral when theexpansive clay mineral reaches the swell potential. In one embodiment,the final water content of the expansive clay mineral is determinedexperimentally following a swell potential test of the expansive claymineral. In another embodiment, the final water content of the expansiveclay mineral is determined by performing a similar forcefield-modifiedmolecular level simulation based on the first water content as aninitial water content and the CEC of the expansive clay mineral.

Whether the initial water content is the second water content todetermine the swell potential of the wetted expansive clay mineralwithout the cementation materials and with Na⁺ as the only exchangeablecation by the forcefield-modified molecular level simulation, or theinitial water content is the first water content to determine the swellpotential and the final water content of the expansive clay mineralwithout the cementation materials and with Na⁺ as the only exchangeablecation by another forcefield-modified molecular level simulation, in oneembodiment, the swell cutoff point is reached when a Monte Carlosimulation step during the molecular level simulation of water sorptiononto the compacted unit cell of the expansive clay mineral at the firstconfining pressure or the stress relaxed unit cell of the expansive claymineral at the second confining pressure results in an increase of about1-5% (w/w), or preferably about 2-4% (w/w) in the water content of theswollen compacted unit cell of the expansive clay mineral or the swollenstress relaxed unit cell of the expansive clay mineral. In anotherembodiment, the molecular level simulation of water sorption onto andswelling of the stress relaxed unit cell at the second confiningpressure further comprises determining a dry density and/or a totalcohesive energy density (TOED) of the swollen stress relaxed unit cellof the expansive clay mineral, and the swell cutoff point is reachedwhen the dry density of the swollen stress relaxed unit cell of theexpansive clay mineral is in the range of 0.1-0.8 g/cm³, 0.2-0.6 g/cm³,or 0.3-0.5 g/cm³, or the TCED of the swollen stress relaxed unit cell ofthe expansive clay mineral is in the range of 1×10⁸-8×10⁸ J/m³,3×10⁸-6×10⁸ J/m³, or 4×10⁸-5×10⁸ J/m³.

In another embodiment, the expansive clay mineral comprises at least oneof the cementation materials of calcite, gypsum, and KCl, and/or atleast one of exchangeable IC, exchangeable Ca²⁺, and exchangeable Mg²⁺,for example, by incorporation of one or more of the cementationmaterials as the swelling reduction agent and/or one or more of theexchangeable K⁺, Ca²⁺, and Mg²⁺ cations as the swelling reduction agentinto the expansive clay mineral. Wetting the swelling reduction agentincorporated expansive clay mineral with water to form the wettedswelling reduction agent incorporated expansive clay mineral with asecond water content higher than the first water content can furtherreduce the swell potential of the expansive clay mineral. In this case,compared to the forcefield-modified molecular level simulation for theexpansive clay mineral that does not contain cementation materials andcontains Na⁺ as the only exchangeable cation described above, theforcefield-modified molecular level simulation may further comprise amolecular level simulation of replacing 0-100% of the total number ofnon-K⁺, Mg²⁺, and Ca²⁺ exchangeable cations (i.e. Na⁺ in this case) witha chosen amount of exchangeable K⁺, Mg²⁺, and/or Ca²⁺ cations in acrystallite of the expansive clay mineral followed by the molecularlevel simulation of water sorption onto the crystallite of the expansiveclay mineral comprising the exchangeable K⁺, Mg²⁺, and/or Ca²⁺ cations(but without the cementation materials yet) to form a water sorbedcrystallite of the expansive clay mineral comprising the exchangeableK⁺, Mg²⁺ and/or Ca²⁺ cations with the second water content as theinitial water content, and may still father comprise a molecular levelsimulation of sorption of the cementation materials, e.g. calcite,gypsum, and/or KCl, in amounts proportional to their weight percentagesin the swelling reduction agent onto the water sorbed crystallite of theexpansive clay mineral comprising the exchangeable K⁺, Mg²⁺, and/or Ca²⁺cations with the second water content as the initial water content. Therest of the forcefield-modified molecular level simulation will be thesame as that for the swelling reduction agent incorporated expansiveclay mineral described in the first aspect of the present disclosure.

As in the method of the first aspect, the pre-set level T in the methodof this aspect, in one embodiment, may be set based on an acceptablelevel of swell potential of the expansive clay mineral, for example, alevel at which the expansive clay mineral may not exert enough force ona building or other structure built on or within the expansive claymineral to cause damage, such as 5-10%, 6-9%, or 7-8%. In someembodiments, the building or other structure built on or within theexpansive clay mineral includes, without limitation, a buildingfoundation, a railway line foundation, a pipe, a footing, a landfillliner, a nuclear waste storage containment liner, a swimming pool, awall, a driveway, a road, a pavement, a basement floor, and a wellbore.

In a preferred embodiment, the wetting of the expansive clay mineral isperformed in a controlled manner, for example, by pre-estimating theamount of water needed and/or by applying (e.g. spraying or injecting)the water to the expansive clay mineral while monitoring the watercontent of the wetted expansive clay mineral, so that the wettedexpansive clay mineral reaches the second water content that is higherthan the first water content.

In some embodiments, an increase of 2-30 percentage points, 4-25percentage points, 6-20 percentage points, 8-15 percentage points, or10-12 percentage points in the water content of the expansive claymineral may result in a 7-60%, 10-50%, 15-40%, or 20-30% reduction inthe swell potential of the expansive clay mineral, depending on the typeof the expansive clay mineral, the types and proportions of exchangeablecations in the expansive clay mineral, and the CEC and initial watercontent of the expansive clay mineral, according to theforcefield-modified molecular level simulation of the presentdisclosure.

After the expansive clay mineral is wetted to reach the higher secondwater content and have the reduced swell potential S_(w) no greater thanthe pre-set level T, in a preferred embodiment, the method furthercomprises maintaining or controlling the water content of the wettedexpansive clayey mineral, to keep the wetted expansive clay mineral at arelatively constant level of water content. One way to keep the wettedexpansive clay mineral at a relatively constant level of water contentmay be by injecting water into the wetted expansive clay mineral at aplurality of injection points, with the amount of water determined basedon the season and humidity. Preferably, periodic measurement of thewater content of the wetted expansive clay mineral is performed so thatthe amount of water injected can be adjusted accordingly.

According to a third aspect, the present disclosure relates to a methodof reducing the swell potential of an expansive clayey soil comprisingat least one expansive clay mineral. The proportion of the weight of theat least one expansive clay mineral relative to the total weight of theexpansive clayey soil is P_(ECM). The expansive clayey soil has a watercontent and a cation exchange capacity (CEC). The method includes (a)carrying out a forcefield-modified molecular level simulation todetermine an amount of a swelling reduction agent to be incorporatedinto the expansive clayey soil to form a swelling reduction agentincorporated expansive clayey soil with a reduced swell potentialS_(i(soil)) that is no greater than a pre-set level T*, wherein theswelling reduction agent incorporated expansive clayey soil comprises aswelling reduction agent incorporated at least one expansive claymineral having a swell potential represented by S_(i(ECM)) andS_(i(soil)) equals S_(i(ECM))×P_(ECM), wherein the swelling reductionagent comprises at least one cementation material selected from thegroup consisting of calcite, gypsum, and potassium chloride at a firstweight percent of the amount of the swelling reduction agent, and/or atleast one exchangeable cation selected from the group consisting of K⁺,Ca²⁺, and Mg²⁺ at a second weight percent of the amount of the swellingreduction agent, wherein the sum of the first weight percent and thesecond weight percent is no greater than 100%, wherein theforcefield-modified molecular level simulation comprises molecularmechanics, molecular dynamics, and Monte Carlo simulation techniquesconfigured to simulate the swell potential of the swelling reductionagent incorporated at least one expansive clay mineral S_(i(ECM)) basedon the water content as an initial water content and CEC of theexpansive clayey soil, the at least one cementation material at thefirst weight percent of the amount of the swelling reduction agent,and/or the at least one exchangeable cation at the second weight percentof the amount of the swelling reduction agent, and (b) incorporating theamount of the swelling reduction agent into the expansive clayey soil toform the swelling reduction agent incorporated expansive clayey soil.

The method of this aspect is similar to the method of the first aspectin that the forcefield-modified molecular level simulation procedure fordetermining the swell potential of the swelling reduction agentincorporated expansive clay mineral(s) (S_(i(ECM))) in the expansiveclayey soil based on the water content and the CEC of the expansiveclayey soil in the method of this aspect is almost identical to that fordetermining the swell potential of the swelling reduction agentincorporated expansive clay mineral based on the water content and theCEC of the expansive clay mineral in the method of the first aspect,except for an adjustment in calculating the amount of the cementationmaterials (e.g. calcite, gypsum, and KCl) as the swelling reductionagent sorbed onto the water sorbed crystallite of the expansive claymineral(s) in the expansive clayey soil based on P_(ECM) as describedbelow. Additionally, the ways of incorporating the swelling reductionagent(s) into the expansive clayey soil, and the types, characteristics,and preferred amount ranges of the swelling reduction agents of themethod of this aspect are the same as those of the method of the firstaspect of the disclosure. However, the method of this aspect reduces theswell potential of an expansive clayey soil comprising expansive claymineral(s), whereas the method of the first aspect reduces the swellpotential of an expansive clay mineral or a mixed expansive clay mineralof different types. Besides the expansive clay minerals, the expansiveclayey soil may further comprise additional minerals and materials, andat least some of the additional minerals and materials may not expand inthe presence of moisture. The swell potential of the expansive clayeysoil is determined by the types and weight percentages of the expansiveclay minerals, the types and weight percentages of non-swellcementitious minerals (e.g. calcite and gypsum), and the types andweight percentages of non-expansive clay minerals (e.g. kaolinite). Thecompositions of an expansive clayey soil, including the types and weightpercentages of expansive clay minerals and non-expansive clay minerals,the types and weight percentages of non-clay, non-swell cementitiousminerals (e.g. calcite and gypsum), and the weight percentage of quartz(sand) in an expansive clayey soil, can be determined by a mineralogicalanalysis using, for example, powder X-ray diffraction (XRD) as shown inTable 6 in the “Examples” of the present disclosure, scanning electronmicroscopy (SEM) with associated energy dispersive micro analysis (EDA),optical microscopy and petrographic analysis. In some embodiments, theproportion of the weight of the expansive clay mineral(s) relative tothe total weight of the expansive clayey soil P_(ECM), or the weightpercentage of the expansive clay mineral(s) (e.g. smectite and illite)in the expansive clayey soil is 5-80%, 10-70%, 20-60%, or 30-50%. Insome embodiments, the weight percentage of non-swell cementitiousminerals in the expansive clayey soil is 1-50%, 10-40%, or 20-30%.

Assuming that the components of the swelling reduction agentincorporated expansive clayey soil other than the expansive claymineral(s) and the swelling reduction agent(s) listed above, such asnon-expansive clay minerals and other non-clay minerals do notcontribute to or affect the swelling process but produce a dilutioneffect proportional to their weight percentages, the effective amount ofcalcite, gypsum, and/or KCl as the swelling reduction agent incorporatedinto the expansive clay mineral(s) of the expansive clayey soil equalsthe input amount×P_(ECM), and the swell potential of the swellingreduction agent incorporated clayey soil S_(i(soil)) equalsS_(i(ECM))×P_(ECM). For example, if the proportion P_(ECM) or weightpercent of the expansive clay mineral(s) is 20% of the total weight ofthe expansive clayey soil, and calcite is present in a calciteincorporated expansive clayey soil at 30% of the total weight of thecalcite incorporated expansive clayey soil, the amount of calciteincorporated into the expansive clay mineral(s) for theforcefield-modified molecular level simulation will be 0.3×0.2=0.06 or6%, and S_(i(soil)) equals S_(i(ECM))×0.2.

In some embodiments, the expansive clayey soil comprises at least oneexpansive clay mineral selected from the group consisting of smectite,bentonite, montmorillonite, beidellite, vermiculite, attapulgite,nontronite, illite, and chlorite.

In some embodiments, the swell potential of the expansive clayey soil is1-404/0, 5-30%, or 10-20%.

The pre-set level T*, in one embodiment, may be set based on anacceptable level of swell potential of the expansive clayey soil, forexample, a level at which the expansive clayey soil may not exert enoughforce on a building or other structure built on or within the expansiveclayey soil to cause damage, such as 5-10%, 6-9%, or 7-8%. In someembodiments, the building or other structure built on or within theexpansive clayey soil includes, without limitation, a buildingfoundation, a railway line foundation, a pipe, a footing, a landfillliner, a nuclear waste storage containment liner, a swimming pool, awall, a driveway, a road, a pavement, a basement floor, and a wellbore.

Since the forcefield-modified molecular level simulation advantageouslypredicts the behavior of real fabric and structure of soil in a preciseand rational manner as compared to all the existing molecular levelmodels for expansive clayey soils, in one embodiment, the expansiveclayey soil is a laboratory compacted expansive clayey soil. In anotherembodiment, the expansive clayey soil is a natural undisturbed expansiveclayey soil.

When an expansive clayey soil also comprises sand, particularly a largepercentage of sand (e.g. at least 50 wt %, at least 60 wt %, or at least70 wt % of the total weight of the expansive clayey soil), the expansiveclayey soil may have a relatively open fabric containing relativelylarge sized pores as compared to an expansive clayey soil containing,for example, 100 wt % of expansive clay minerals, indicating a betterwater permeability favoring a complete swelling of all the expansiveclay minerals present in the soil fabric, Thus, when the expansiveclayey soil also comprises sand, all or a portion of the sand ispreferably removed from the expansive clayey soil prior to incorporatingthe swelling reduction agent, particularly calcite, gypsum, and/or KClthat provide binding or cementation effects to the individual or groupof the expansive clay mineral particles, into the expansive clayey soilto reduce the swell potential of the expansive clayey soil. This isespecially advantageous when the volume and/or weight percentage of thesand in the expansive clayey soil is big. Removing all or a portion ofthe sand facilitates the contact of the swelling reduction agent withthe expansive clay minerals and may require a smaller amount of theswelling reduction agent to make the swell potential of the swellingreduction agent incorporated expansive clayey soil no greater than thepre-set level T*. In one embodiment, the sand may be separated andremoved from the expansive clayey soil with one or more soil screensieves. For example, the expansive clayey soil that preferably has beendried and broken up into loose particles may be passed through a soilscreen sieve, or more preferably a set of soil screen sieves with themesh sizes of, for example, #5, #10, #60, and #230 (mesh size is anindication of number of openings per linear inch) and arranged with thesoil screen sieve of the largest screen size (e.g. the #5 mesh sizescreen) on top followed by the soil screen sieves of proportionatelydecreasing screen sizes to a closed bottom container, preferably withshaking. As a result, the expansive clayey soil particles that remain onthe first sieve of the #5 mesh size are gravels. The expansive clayeysoil particles that remain on the second sieve of the #10 mesh size arefine gravels. The expansive clayey soil particles that remain on thethird sieve of the #60 mesh size are coarse sand. The expansive clayeysoil particles that remain on the fourth sieve of the #230 mesh size arefine sand. The expansive clayey soil particles that are collected in theclosed bottom container are silt and clay. The total mass of theexpansive clayey soil processed by the soil screen sieves and the massof the sand particles are preferably measured by a scale or a balance sothat the weight percent of the sand present in or removed from theexpansive clayey soil can be determined. In some embodiments, replacingthe sand at an amount of 10-50 wt % of the total weight of the expansiveclayey soil with the same mass of gypsum may reduce the swell potentialof the expansive clayey soil 60-95%, or 70-90%, or 80% based on theactual swell potential tests performed in the present disclosure andshown in the Examples. In other embodiments, replacing the sand at anamount of 30-50% of the total weight of the expansive clayey soil withthe same mass of calcite may reduce the swell potential of the expansiveclayey soil 20-60%, 30-50%, or 40% based on the actual swell potentialtests performed in the present disclosure and shown in the Examples.

In another preferred embodiment, all or a portion of the sand removedfrom the expansive clayey soil may be replaced by at least onenon-expansive clay mineral, such as kaolinite, mica, hydroxyinterlayered vermiculite (HIV), and hydroxy interlayered smectite (HIS),prior to incorporating the swelling reduction agent into the expansiveclayey soil, probably because a non-expansive clay mineral likekaolinite has a fine grained texture with a low water permeability ascompared to sand. In some embodiments, replacing the sand at an amountof 20-40%, 25-35%, or 30% of the total weight of the expansive clayeysoil with the same mass of kaolinite may reduce the swell potential ofthe expansive clayey soil 10-30%, 15-25%, or 20% based on the actualswell potential tests performed in the present disclosure and shown inthe Examples.

According to a fourth aspect, the present disclosure relates to a methodof reducing the swell potential of an expansive clayey soil comprisingat least one expansive clay mineral by wetting the expansive clayeysoil. The proportion of the weight of the at least one expansive claymineral relative to the total weight of the expansive clayey soil isP_(ECM). The expansive clayey soil has a first water content and acation exchange capacity (CEC). The method includes (a) carrying out aforcefield-modified molecular level simulation to determine a secondwater content of a wetted expansive clayey soil to be formed by wettingthe expansive clayey soil with water, wherein the wetted expansiveclayey soil has a reduced swell potential S_(w(soil)) that is no greaterthan a pre-set level T* and comprises wetted at least one expansive claymineral having a swell potential represented by S_(w(ECM)), whereinS_(w(soil)) equals S_(w(ECM))×P_(ECM), wherein the forcefield-modifiedmolecular level simulation comprises molecular mechanics, moleculardynamics, and Monte Carlo simulation techniques configured to simulatethe swell potential of the wetted at least one expansive clay mineralS_(w(ECM)) based on the cation exchange capacity (CEC) of the expansiveclayey soil and the second water content of the wetted expansive clayeysoil as an initial water content (IWC), wherein the second water contentas the initial water content (IWC) is greater than the first watercontent but no greater than a final water content (FWC) of the at leastone expansive clay mineral when the at least one expansive clay mineral(as well as the expansive clayey soil the at least one expansive claymineral resides in) reaches the swell potential, and (b) wetting theexpansive clayey soil with water to form the wetted expansive clayeysoil having the second water content and the reduced swell potentialS_(w(soil)).

The method of this aspect is similar to the method of the second aspectin that the forcefield-modified molecular level simulation procedure fordetermining the swell potential of the wetted at least one expansiveclay mineral in the expansive clayey soil represented by S_(w(ECM))based on the second water content of the wetted expansive clayey soil asan initial water content (IWC) and the CEC of the expansive clayey soilin the method of this aspect is identical to that for determining theswell potential of the wetted expansive clay mineral represented byS_(w) based on the second water content of the wetted expansive claymineral as the initial water content and the CEC of the expansive claymineral in the method of the second aspect, with the swell potential ofthe wetted expansive clayey soil S_(w(soil)) equaling S_(w(ECM))×P_(ECM)based on the assumption that the components of the expansive clayey soilother than the expansive clay mineral(s) and the swelling reductionagent(s), such as non-expansive clay minerals and other non-clayminerals do not contribute to or affect the swelling process but producea dilution effect proportional to their weight percentages.

As in the method of the third aspect, the pre-set level T* in the methodof this aspect, in one embodiment, may be set based on an acceptablelevel of swell potential of the expansive clayey soil, for example, alevel at which the expansive clayey soil may not exert enough force on abuilding or other structure built on or within the expansive clayey soilto cause damage, such as 5-10%, 6-9%, or 7-8%. In some embodiments, thebuilding or other structure built on or within the expansive clayey soilincludes, without limitation, a building foundation, a railway linefoundation, a pipe, a footing, a landfill liner, a nuclear waste storagecontainment liner, a swimming pool, a wall, a driveway, a road, apavement, a basement floor, and a wellbore.

In some embodiments, an increase of 2-30 percentage points, 4-25percentage points, 6-20 percentage points, 8-15 percentage points, or10-12 percentage points in the water content of the expansive clayeysoil may result in a 5-95%, 10-90%, 15-85%, 20-80%, 30-70%, 40-60%, or50% reduction in the swell potential of the expansive clayey soil,depending on the initial water content of the expansive clayey soil, theweight percent of the expansive clay minerals in the expansive clayeysoil or P_(ECM), and the weight percent of sand in the expansive clayeysoil.

As in the method of the second aspect, the wetting of the expansiveclayey soil is preferably performed in a controlled manner, for example,by pre-estimating the amount of water needed and/or by applying (e.g.spraying or injecting) the water to the expansive clayey soil whilemonitoring the water content of the wetted expansive clayey soil, sothat the wetted expansive clayey soil reaches the second water contentthat is higher than the first water content. Additionally, the highersecond water content achieved by the wetting of the expansive clayeysoil preferably needs to be maintained or stabilized, for example, bysubgrade irrigation when the wetted expansive soil is used as foundationsoil. Subgrade irrigation involves the installation of pipes to conductwater into the foundation soil at various injection points. The amountof water required depends on the season and the humidity. Periodicmeasurement of the wetted expansive clayey soil moisture may be requiredso that the amount of water injected can be adjusted accordingly. Thesource of water may be a well or the domestic water supply.

In case wetting the expansive clayey soil alone to reduce its swellpotential to a level no greater than the pre-set level T* is notfeasible, e.g. the second water content needed to reduce the swellpotential of the expansive clayey soil to no greater than the pre-setlevel T* based on the forcefield-modified molecular level simulation isgreater than the final water content, or the second water content isconsidered too high to be maintained practically, incorporating theswelling reduction agent(s) into the expansive clayey soil, andoptionally removing sand and/or replacing sand with non-expansive clayminerals described in the third aspect of the present disclosure may becombined with the wetting. The forcefield-modified molecular levelsimulation for determining the amount of the swelling reduction agentthat includes the exchangeable K⁺, Ca²⁺, and/or Mg²⁺ and/or thecementation materials of calcite, gypsum, and KCl is identical to theforcefield-modified molecular level simulation described in the thirdaspect, with the second water content as the initial water content.

An expansive clayey soil that has expanded or swelled due to a highground moisture or has been wetted experiences a loss of soil strengthor “capacity” and the resulting instability can result in various formsof problems and/or failures of the structures built on or within theexpansive clayey soil. In a preferred embodiment, the wetted and/orswelling reduction agent incorporated expansive clayey soil is furthertreated or incorporated with at least one soil stabilization materialselected from ground granulated blastfurnace slag (GOBS), cement,resins, fly ash, lime, pozzolana, and a mixture of lime and pozzolana.In some embodiments, a mixture of ground granulated blastfurnace slag(GGBS) and gypsum, preferably red gypsum, may be incorporated into a(wetted) expansive clayey soil, with the weight ratio of the gypsum:theGGBS in the mixture in the range of 1:5 to 5:1, 1:4 to 4:1, preferably1:3 to 3:1, more preferably 1:3 to 3:2, or more preferably 1:4 to 2:3,with the pH of the mixture preferably adjusted by lime to be greaterthan 10.5, or preferably greater than 12, to increase the strength ofthe (wetted) expansive clayey soil as well as decrease the swellpotential of the (wetted) expansive clayey soil. In a preferredembodiment, the amount of the gypsum determined to be incorporated intothe (wetted) expansive clayey soil according to the forcefield-modifiedmolecular level simulation is 20-50%, or 20-40% of the total weight ofthe (wetted) swelling reduction agent incorporated expansive clayeysoil, with the co-incorporated GGBS at an amount of 15-60%, 20-50%, or30-40% of the total weight of the (wetted) swelling reduction agentincorporated expansive clayey soil, and the co-incorporated lime at anamount of 0.1-5%, or 0.5-3% of the total weight of the (wetted) swellingreduction agent incorporated expansive clayey soil.

Having generally described this invention, a further understanding canbe obtained by reference to certain specific examples which are providedherein for purposes of illustration only and are not intended to belimiting unless otherwise specified.

Examples LIST OF ABBREVIATIONS CEC Cation Exchange Capacity CED CohesiveEnergy Density CT Computed Tomography EDS Energy Dispersive SpectroscopyESEM Environmental Scanning Electron Microscope FTIR Fourier TransformInfrared Spectroscopy LJ Lennard Jones LL Liquid Limit MC Monte Carlo MDMolecular Dynamics MM Molecular Mechanics NPT Constant Number ofParticles, Pressure, and Temperature Ensemble PI Plasticity Index PLPlastic Limit OMC Optimum Moisture Content XRD X-Ray Diffraction

The methodology of the examples covered three major levels ofactivities; macro level testing, micro level imaging and analysis, andmolecular level simulation and modeling. The research methodologygenerally involved formulation of several types and nature offabrics/structures of expansive clays through preparation and compactionof mixes of expansive clay minerals and non-expansive/non-clay mineralsin various proportions at several moisture and density conditions,mapping and analysis of the fabric and structure of the laboratorycompacted expansive clays specimens using nano/micro level imaginglaboratory techniques at the pre and post swelling states. This wasachieved through advanced imaging techniques such as X-ray diffraction(XRD), Environmental SEM (ESEM), Fourier Transform Infrared Spectroscopy(FTIR), and Computerized X-ray Tomography (Micro CT). Finally, toprecisely model the behavior of natural and compacted fabric andstructure of the expansive clays, molecular scale simulation of theswelling behavior of the above mentioned natural and compacted fabricand structure was carried out using the concepts of molecular mechanics(MM) molecular dynamics (MD) and Monte Carlo (MC) simulation techniques.

One of the objectives of this disclosure is to compare the behavior ofthe natural expansive clay deposits and the laboratory reconstitutedspecimens using controlled proportions of the standard soil constituentswith the simulation models. Therefore, to constitute the control samplesbesides obtaining undisturbed samples from natural expansive soildeposits, individual soil constituents were also acquired fromstandard/known sources.

Qatif and Hofuf areas in the eastern region of Saudi Arabia are wellknown for the presence of problematic shallow subsurface expansive soilsdeposits. Sampling plan was prepared to acquire representativeundisturbed samples from some of the sites in Hofuf and Qatif known fortheir volume change behavior. For the purpose, test pits were excavatedin the shallow subsurface to expose the expansive soil layers. Largelumps/pieces of expansive clayey soils were acquired from the excavatedtest pits and were immediately sealed to preserve the natural moisturecontent of these samples. Two samples each representative of twodifferent expansive clay deposits were acquired from Qatif area, whileone sample was obtained from Hofuf area. Samples from Qatif area wereobtained from a site in the housing area next to Qatif Central Hospital,while sample from Hofuf area was acquired from a site in National Guard.The samples were characterized using various laboratory index tests andXRD and the results are summarized in Tables 4, 5, and 6.

TABLE 4 Summary of index tests on the acquired samples and materialsSpecific Atterberg Limits Surface CEC Material Designation SourceClassification LL PL PI Area (m²/g) (meq/100 g) Na-Montmorillonite NaMThe Clay Mineral CH 612 36 576 31.82 76.4 (SWy-1) Society, USCa-Montmorillonite CaM The Clay Mineral MH 129 55 74 97.42 120.0 (SAz-1)Society, US Kaolinite (KGa-1) K The Clay Mineral MH 58 36 22 10.05 2.0Society, US Bentonite B Kanoo Est., KSA CH 480 44 436 — 54.8 QatifClay-Source 1 Q-1 Qatif, KSA CH 155 53 102 — 51.0 Qatif Clay-Source 2Q-2 Qatif, KSA CH 69 29 40 — 20.7 Hofuf Clay H-1 Hofuf, KSA CH 70 27 43— 12.7 Calcium Cabonate Ca Techno — — — — — — Pharmchem, India Gypsum GPhosphate Plant, — — — — — — RIC, KSA Sand S Jubail, KSA SP NP NP NP — —CH: High Plastic CLAY MH: Elastic SILT SP: Poorly graded SAND NP: NonPlastic RIC: Ras al-Khair Industrial City KSA: Kingdom of Saudi ArabiaAtterberg Limits methodology: ASTM D 4318 Specific Surface Areamethodology: Brunauer, Emmett and Teller (BET) Method CEC methodology:Payment and Higginson (1992)

TABLE 5 Exchangeable and total cations analysis of the Clay samplesExchangeable Cations Total Cations CEC % of % of Fixed Soil Designation(meq/100 g) Type meq/100 g mg/kg CEC Type mg/kg Cations Bentonite B 54.8Ca 35.2 7054 64 Ca 16300 22 Mg 2.4 292 4 Mg 869 1 K 2.0 782 4 K 1200 1Na 15.2 3496 28 Na 24300 49 Qatif Clay-Source 1 Q-1 51.0 Ca 25.0 5004 49Ca 101000 68 Mg 17.0 2002 33 Mg 32400 22 K 7.0 2963 14 K 6280 2 Na 2.0496 4 Na 840 0 Qatif Clay-Source 2 Q-2 20.7 Ca 10.0 2004 48 Ca 118000 54Mg 7.0 851 34 Mg 89600 41 K 3.0 1173 14 K 6920 3 Na 0.7 161 3 Na 1540 1Hofuf Clay H-1 12.7 Ca 7.2 1443 57 Ca 28000 54 Mg 4.1 510 32 Mg 8900 17K 1.2 469 9 K 6880 13 Na 0.2 46 2 Na 5790 12 Total Cations methodology:APHA 21^(e) ed., USEPA SW 846-6010 (ICPAES)

TABLE 6 Mineralogical analysis of Clay samples Soil Designation SmectiteKaolinite Illite Palygorskite Quartz Calcite Dolomite GypsumNa-Montmorillonite (SWy-1) NaM 97 — — — 3 — — — Ca-Montmorillonite(SAz-2) CaM 95 — — — 5 — — — Bentonite B 95 — — — 5 — — — QatifClay-Source 1 Q-1 32 — 21 7 9 22 — 9 Qatif Clay-Source 2 Q-2 15 — 25 915 — 24 12 Hofuf Clay H-1 — 5 35 5 15 40 — —

In order to precisely isolate and study the relative contribution ofvarious non-swelling clay particles/minerals to the behavior of swellingclay minerals, several standard materials were acquired from the knownsources. These materials were further characterized to define thepertinent properties and complete compositional details. For thepurpose, samples of standard clay minerals of different composition wereobtained from Clay Mineral Society. See Clay Minerals Society (2013),“Source Clays Physical/Chemical Data”,http://www.clays.org/SOURCE%20CLAYS/SCdata.html, incorporated herein byreference in its entirety. Na-montmorillonite (SWy-1),Ca-montmorillonite (SAz-1), and Kaolinite (KGa-1) are the three standardclay samples obtained from Clay Mineral Society.

As only small quantities of samples are available with Clay MineralSociety and large quantities were required to perform the requiredexperimentation, commercially available bentonite samples were alsoobtained from Kanoo establishment, one of the bentonite (drilling mud)suppliers in KSA. As per information provided by the supplier, thesource of this bentonite is from the shale deposits in Gujrat city ofIndia. The bentonite is quarried from these deposits, crushed to finepowder (passing Sieve No. 200), homogenized, and marketed in 50 lbsbags. For this study, five bentonite bags were obtained from thesupplier and were stored in controlled temperature and humidity rooms.Several samples were collected from different parts of the bags for thecharacterization and further verification of the homogeneity anduniformity of the bag samples. The test results indicate a uniformlydistributed material throughout the bags.

In addition to the standard clay minerals from Clay Mineral Society andcommercial bentonite, sand samples were acquired from the general sanddune deposits near Jubail area of KSA. Bulk sand samples were sampledand were washed through the sieves (No. 4 to No. 200). The relativeamount of material retained on each sieve was collected andreconstituted to a standard gradation (Table 7).

TABLE 7 Standard gradation for the Sand sample ASTM Sieve No. 10 20 4060 100 200 % passing 100 92 58 35 19 2

In any typical natural expansive clayey soil deposit, in addition toswelling and non-swelling clay minerals, other common inclusions arequartz (sand), gypsum and calcite. In order to constitute controllaboratory samples, these inclusions such as gypsum and calciumcarbonate were also acquired from the known/standard sources. Each ofthese materials were further characterized using XRD and chemicaltesting techniques for verification of the composition. Gypsum sampleswere acquired in powdered form from Ma'aden's Phosphoric Acid Plant atRas al-Khair on the east coast of KSA. Calcium carbonate was obtainedfrom the local market manufactured by Techno Pharmchem, India.Characterization results for these materials are presented in Tables 4,5, and 6.

The control laboratory specimens were prepared at various moisturecontents using the distilled water and compacted at various densitiesusing both static and dynamic compaction techniques. Detailed steps andprocedures for the sample preparations in the laboratory are providedherein.

In order to formulate the various forms of fabric and structure, controlspecimens with known proportions of clay minerals and non-clayminerals/particles were prepared at various known densities and moisturecontents. Types of clay and non-clay constituents and the correspondingproportions used for preparing the controlled specimens are listed inTable 8.

TABLE 8 List of control samples with the details of the respectivecompositions of various constituents. Sample Moisture No Content StateNaM CaM Bentonite Sand Gypsum Calcite Kaolinite 1 Dry of OMC — — 100 — —— — 2 Wet of OMC — — 100 — — — — 3 Dry of OMC — — 60 40 — — — 4 Wet ofOMC — — 60 40 — — — 5 Dry of OMC — — 30 70 — — — 6 Wet of OMC — — 30 70— — — 7 Dry of OMC — — 10 90 — — — 8 Wet of OMC — — 10 90 — — — 9 Dry ofOMC* — — 30 70 — — — 10 Dry of OMC* — — 30 60 10 — — 11 Dry of OMC* — —30 40 30 — — 12 Dry of OMC* — — 30 20 50 — — 13 Dry of OMC* — — 30 40 —30 — 14 Dry of OMC* — — 30 20 — 50 — 15 Dry of OMC* — — 30 40 — — 30 16Dry of OMC* — — — — — — 100 17 Dry of OMC* — — — 40 — — 60 18 Dry ofOMC* — — — 70 — — 30 19 Dry of OMC* 100 — — — — — — 20 Dry of OMC* 60 —— 40 — — — 21 Dry of OMC* 30 — — 70 — — — 22 Dry of OMC* — 100 — — — — —23 Dry of OMC* — 60 — 40 — — — 24 Dry of OMC* — 30 — 70 — — — *StaticCompetition

In this study, baseline mixtures were prepared using bentonite and sandin various proportions (10, 30, 60, and 100% bentonite) and themoisture-density relationships were developed for each of the proportionusing modified Proctor Test procedure (ASTM D 1557). Proctor testprovides a relationship between moisture and density with its peakdensity at optimum moisture content (OMC) and further marking differentzones such as dry and wet side of optimum moisture content. Results ofProctor compaction tests are provided in FIG. 31. To formulate specimenswith different fabric conditions, specimens were prepared at 95% ofmaximum dry density both on dry and wet side of OMC. For the purpose,samples were prepared by mixing the required proportions of clay, sand,and water and were left over in sealed plastic bags for a minimum periodof twenty four hours. This is to ensure the proper and uniformdistribution and adsorption of the moisture throughout the clay and sandparticles. These loose mixed samples were then compacted to 95% maximumdry density in the Proctor mold. Oedometer circular steel rings of 70 mmdiameter and 19 mm height were then hydraulically pushed into thecompacted samples to obtain the required specimens. The compactedspecimens along with the rings were sealed against moisture loss foronward testing for the swelling tests. Among these specimens, one with30% bentonite and compacted at 95% maximum dry density on the dry sideof the OMC was selected as a reference specimen for the furthervariation in the clay and non-clay constituents.

As samples of standard materials other than bentonite could not beobtained in ample quantities for the dynamically compacted specimens, itwas decided to use static compaction technique for the rest of thevariation in constituents. For the comparison purpose, referencespecimen (30% bentonite) was also compacted to the required density (95%of maximum dry density) on dry side of OMC using static compactiontechnique in the oedometer rings. The specimens were compacted in twolayers through the piston of the compression machine having almost thesame diameter as of the oedometer ring. Equivalent static pressure toachieve the same density in oedometer rings as in Proctor compaction wasdetermined to be 1500 kPa. This equivalent pressure was used to compactthe mixes in which sand was partially replaced with other constituents,several combinations used are listed in Table 8. In order to achieve therequired density and moisture conditions, the samples were compacted toa pressure of 1500 kPa. In order to preserve the moisture conditions,the compacted specimens were immediately sealed with several wraps ofplastic cling film and cased in polythene bags. In addition to thespecimen compacted for swelling test, additional similar specimens wereprepared for the micro investigation on the pre swell samples. These preswell samples, taken from the compacted layer, were later on evaluatedusing molecular/nano level investigation and imaging techniques. All thelaboratory prepared specimens were subjected to swell potential tests asdetailed below.

Specimens for the swell potential tests were prepared with variousproportions of bentonite, sand, and/or gypsum, calcite, and kaolinite.Similarly, standard clays were also mixed with 40% and 70% sand andcompacted to the maximum density corresponding to 1500 kPa staticpressure. In order to ensure that specimens of standard clays becompacted on the dry side of OMC, it was assessed from the PL of theseclay samples. Swell potential tests were carried out in generalagreement with ASTM D 5890 and compacted specimens were subjected tofree swell testing in the oedometer test equipment. In order to magnifythe relative influence of each change in type and percentage ofnon-swell particles, the specimens were surcharged with a low surchargepressure of 2 kPa and flooded with distilled water in the oedometerspecimen holder. Increase in height of the specimen was recorded atregular time intervals until no further noticeable change in height ofthe specimen is recorded. Maximum change in the height of the specimendivided by the original height was recorded and expressed in percentswell for each tested specimen. After the swelling test, samples formoisture content were cut from the middle of the ring and rest waspreserved for the post-swell micro level imaging and tests. The resultsof the swell tests carried out on bentonite, sand, and other inclusionsare summarized in Table 9 and plotted in FIG. 22.

TABLE 9 Initial Initial Final Final Sam- Dry Wet Dry Wet ple MoistureSwell Density IMC Density FMC Density Density No. Content State NaM CaMBentonite Sand Gypsum Calcite Kaolinite (%) (g/cm³) (%) (g/cm³) (%)(g/cm³) (g/cm³) 1 Dry of OMC — — 100 — — — — 184 1.290 29.5 1.67 136.00.45 1.07 2 Wet of OMC — — 100 — — — — 132 1.290 39.0 1.79 174.0 0.561.52 3 Dry of OMC — — 60 40 — — — 153 1.577 19.5 1.88 93.0 0.62 1.20 4Wet of OMC — — 60 40 — — — 111 1.577 26.0 1.99 103.0 0.75 1.52 5 Dry ofOMC — — 30 70 — — — 89 1.750 11.3 1.95 72.0 0.93 1.59 6 Wet of OMC — —30 70 — — — 53 1.750 18.8 2.08 82.0 1.14 2.08 7 Dry of OMC — — 10 90 — —— 32 1.917 5.2 2.02 18.0 1.45 1.71 8 Wet of OMC — — 10 90 — — — 5 1.91713.4 2.17 22.0 1.83 2.23 9 Dry of OMC* — — 30 70 — — — 121 1.750 12.01.96 108.0 0.79 1.65 10 Dry of OMC* — — 30 60 10 — — 21 1.750 12.0 1.9656.0 1.45 2.26 11 Dry of OMC* — — 30 40 30 — — 11 1.750 12.0 1.96 27.01.58 2.00 12 Dry of OMC* — — 30 20 50 — — 6 1.750 12.0 1.96 19.0 1.651.96 13 Dry of OMC* — — 30 40 — 30 — 74 1.750 12.0 1.96 80.0 1.01 1.8114 Dry of OMC* — — 30 20 — 50 — 68 1.750 12.0 1.96 66.0 1.04 1.73 15 Dryof OMC* — — 30 40 — — 30 95 1.750 12.0 1.96 115.0 0.90 1.93 16 Dry ofOMC* — — — — — — 100 4 1.512 23.1 1.86 27.0 1.45 1.84 17 Dry of OMC* — —— 40 — — 60 3 1.828 13.3 2.07 16.0 1.77 2.06 18 Dry of OMC* — — — 70 — —30 1 1.845 8.1 1.99 11.0 1.83 2.03 19 Dry of OMC* 100 — — — — — — 961.436 3.8 1.49 87.0 0.73 1.37 20 Dry of OMC* 60 — — 40 — — — 59 1.67310.0 1.84 50.0 1.05 1.58 21 Dry of OMC* 30 — — 70 — — — 25 1.889 8.02.04 25.0 1.51 1.89 22 Dry of OMC* — 100 — — — — 49 1.298 1.5 1.32 90.00.87 1.66 23 Dry of OMC* — 60 — 40 — — — 18 1.567 16.3 1.82 42.0 1.331.89 24 Dry of OMC* — 30 — 70 — — — 9 1.591 11.5 1.77 33.7 1.46 1.95 25NMC Qatif (Q-1) 29 1.367 7.2 1.47 55.6 1.06 1.65 26 NMC Qatif (Q-2) 81.557 5.2 1.64 40.0 1.44 2.02 27 NMC Hofuf (H-1) 5 1.507 3.9 1.57 29.31.44 1.86 *Static Compaction NMC: Natural Moisture Content IMC: InitialMoisture Content FMC: Final Moisture Content

Micro level fabric testing and visualization of the pre and post swellsamples was carried out using X-ray Diffraction (XRD), Fourier TransformInfrared Spectroscopy (FTIR), Micro Computed Tomography Scan (CT), andEnvironmental Scanning Electron Microscopy (ESEM). XRD and CT wereperformed at Center of Excellence in Nanotechnology of KFUPM, while FTIRtests were conducted at the Center for Refining and Petrochemicals ofthe Research Institute (RI) of KFUPM. ESEM were conducted at R&D Centerof Saudi Aramco at Dhahran, KSA. The main objectives achieved throughthis laboratory study were the soil fabric visualization, variation ininterlayer spacing with change in moisture regime, assessment ofcrystallite size, and interaction among swelling and non-swelling soilparticles in the fabric on the dry and wet side of optimum moisturecontent both in pre and post swell state. The molecular levelinformation acquired from these tests was used as an input in themolecular level modeling schemes.

Pre and post swell specimens were tested for mineralogical analysis andchange in interlayer/lattice space at various moisture regimes usingRigaku Miniflex II X-ray Diffraction (XRD) equipment. XRD equipment isequipped with a 40 keV X-ray tube, radiation safe enclosure, waterchiller, and a monochromator.

For the testing purpose, few grams of representative specimen were takenfrom the corresponding samples and were pulverized/smeared to the finepowder or was used in paste form for high moisture content samples. Thepulverized or paste sample was then placed in a sample holder creating aflat upper surface and assuring random distribution of latticeorientation. The specimen was subject to XRD testing from thediffraction angles 2θ varying from 3° to 90°. During the test, intensityof diffracted X-rays was continuously recorded as the sample anddetector rotate through their respective angles. A peak in intensityoccurs when the mineral contains lattice planes with d-spacingsappropriate to diffract X-rays at that value of θ. The data was analyzedto determine the presence of various minerals and their approximatepercentages. The XRD results are presented as peak positions at dspacings and X-ray counts (intensity) in the form of x-y plots in FIGS.104 to 140. These plots were also used to determine the changes inlattice/d-spacing upon change in moisture content in the pre and postswell state.

In addition to the knowledge of type and proportions of various mineralsand the changes in the lattice spacing of clay minerals, crystallitesize was also approximately assessed from XRD data. For the purpose,Scherrer method was used and procedure is shown in FIG. 33. SeeScherrer, P. (1918), “Bestimmung der Grösse and der inneren Struktur vonKolloidteilchen mittels Röntgenstrahlen” Nachr. Ges. Wiss. Göttingen 26(1918) pp. 98-100, incorporated herein by reference in its entirety. Theline broadening caused by small crystal size, B, is calculated using therelation suggested by Warren (see Warren, B. E. (1941), “X-ray methods”,Jour. Applied Physics 12, 375-83, incorporated herein by reference inits entirety),B2=BM2−BS2  3-1

where

BM=measured montmorillonite peak breadth

BS=average measured aluminum peak breadth in radians

The Schemer's formula relating peak breadth to crystal size is,D=0.9λ/(B cos θB)  3-2

where λ=1.542 Å and θB=diffraction angle at maximum intensity

Fourier Transform Infrared Spectroscopy (FTIR) was carried out usingNicolet 6700 FTIR spectrometer at Center for Refining and Petrochemicalsat Research Institute (RI) of KFUPM. The equipment is equipped withOMNIC software and is capable of recording the wavelengths in the rangeof 400 cm-1 and 4000 nm.

For the analysis, few grams of representative sample was obtained fromeach of the pre and post swell samples. These samples were mixed withpotassium bromide (KBr) and mixed thoroughly in a stone dish using themarble pestle. After achieving a uniform color, the mix was placed in asteel mold and the mold was compressed to form a thin slice/pellet. Thepellet was carefully removed from the mold and placed in a verticalstand in the specimen chamber of the equipment. The sample holder wasplaced in such a way that the incident laser beam focuses on thespecimen. OMNIC software is used to control the data acquisition. Toexclude the other possible interferences in the sample chamber,background data is acquired using the software before placing thespecimen. For each specimen, data was acquired for a wavelength range of400 to 4000 cm⁻¹. The data acquired for the specimen is corrected bysubtracting the background from the collected data. The data wasacquired in absorbance units and the final results are presented aswavelength versus absorbance. The FTIR results are shown in FIGS. 141 to168.

The pre and post swell samples obtained from the swell test specimenswere viewed, examined, and studied using Environmental Scanning ElectronMicroscope (ESEM). FEI-Phillips ESEM-FEG Quanta 400 available at R&Dcenter of Saudi Aramco was used for the purpose.

In ESEM, electron guns are used to produce a fine, controlled beam ofelectrons which are then focused at the specimen surface. ESEM mode inthe instrument applies high pressure to ensure prevention of moistureduring the test. In this study, a pressure up to 0.55 torr was used. Theelectron gun emits electrons from field-emission gun to produce an imagerepresenting the morphology of the sample. Moreover, it also facilitatesin the spot and general elemental analysis at the selectedpoints/surface of the specimen.

Representative sample particles/particle assemblage of the pre andpost-swell specimens were placed on the copper strips pasted on thespecimen holders. The specimens were scanned in the ESEM at 20 keV toacquire the high contrasting micrographs at different resolutionsvarying from 100× to 30,000×. Spot and general area level elementalanalysis was also carried out using Energy Dispersive Spectroscopy (EDS)at the selected locations and/or areas of the specimens using 20 keVenergy electron beams. EDS spectrums of several spots on the selectedspecimens were obtained to assess the elemental composition of thespecimen. The ESEM and EDS results are presented FIGS. 169 to 202.

X-ray Computed. Tomography (Micro CT) of the compacted and the naturalclay samples was carried out using Micro CT SkyScan 1172 equipment. Thisequipment is capable of providing tomographic sections of the specimensin 2-D and 3-D with a resolution of 1 micron. The equipment is equippedwith an X-ray source of 100 keV to focus on a spot size of less than 5micron. The associated acquisition and analysis software aid in theacquisition of the data and further analyzing and presenting the data in2-D and 3-D tomographic sections.

Cubical to cylindrical specimens of about 15 mm×25 mm in size were usedfor the CT scanning of the pre and post swell samples. The specimenswere fixed on the sample holder placed in the sample chamber of theequipment. Through the acquisition software, the specimens were focusedto scan the middle section of the specimen without any dried endeffects. The specimens were scanned using X-ray energy of 72 keV andscans were obtained every 2° of the specimen. After the complete scan,data was loaded in the analysis software for display and development oftomographic sections. The raw data was reconstructed to formulate aseries of tomographic sections of the entire height of the specimen.These series of sections were converted to a video form that shows theslides/slices of the variation in the X-ray attenuated sections alongthe height of the scanned specimen. Attenuation of the X-rays, whiletravelling through the specimen, is a result of several factorsincluding density and the nature of the particles. During reconstructionof the specimen tomographic sections, each level of X-ray attenuationwas designated with a different color. Colored CT sections of all thetested specimens, before and after the swell tests are shown in micro CTscan results of FIGS. 203A to 209B.

An objective of the present disclosure is to simulate and study theprocesses and interactions occurring at the molecular level in thenatural and compacted fabrics of the expansive soils. A typical naturalmicrostructure of expansive soils consists of clay and non-clayparticles assemblages, pores varying from nano to micro level, and thewater present in all these pore levels. A particle assemblage furtherconsists of various sizes of the unit crystallites or quasi-crystals ofeach constituent. In the present disclosure, molecular mechanics (MM),molecular dynamics (MD), and Monte Carlo (MC) based simulationtechniques were used to study the interactions between clay and non-clayparticles in the presence of various combinations of interlayer andintra layer cations, anions, and water under various fabric andstructure conditions. Materials Studio software (2013) have been used inthis simulation study. Due to large volume of computations involved inthe simulations, these calculations were carried out through the highperformance computing facilities at KFUPM and King Abdullah Universityof Sciences and Technology (KAUST), KSA; HPC at KFUPM and NESER at KAUSTwere used for the purpose.

The general needs for any molecular simulation scheme are the choice ofthe representative crystallites, formulation of the representative unitcells with periodic boundary conditions, and running the appropriateensemble using an applicable forcefield. The present disclosure alsoinvolved the modifications to the existing Universal force fieldin-built in the software to adapt it to the simulations involved in thepresent disclosure. The steps adopted for the formulation of unit cellsand the subsequent simulations are described below.

In order to formulate the basic unit cells of the soil fabric,individual clay and non-clay crystallites/molecules were acquired fromseveral sources. Unit molecules used in the formulation areNa-montmorillonite of three different Cation Exchange Capacity (CEC),pyrophyllite, kaolinite, calcite (Calcium Carbonate), Calcium Sulfate(Gypsum), Potassium Chloride, and water. Most of these basic molecularunits including two CEC Na-montmorillonite, kaolinite, CalciumCarbonate, and Calcium Sulfate were acquired from Nanoscale SimulationLab at University of Akron, US (2013), while other molecules wereprepared using the drafting tools of the software. See NanoscaleSimulation Lab at University of Akron, US (2013)(http://www2.uakron.edu/cpspe/dpe/web/nsl/interface-force-field.php,incorporated herein by reference in its entirety). The moleculesacquired from Nanoscale simulation lab are already in charged state andtheir charges were verified using charge equilibration method QEq of theMaterials Studio software. Other molecules formulated in the softwarewere charged using QEq module of the software. In order to study therelative effect of CEC on the simulation behavior, Na-montmorillonitemolecules of three different CECs of 54, 90, and 144 meq/100 g wereused. A typical Na-montmorillonite model with CEC of 90 meq/100 g and Naas interlayer cations is shown in FIGS. 34 and 35. In addition,pyrophyllite (CEC=0) known for its non-swell nature, was also used as areference to verify the parameters in the simulation technique. Atypical pyrophyllite crystallite is shown in FIGS. 34 and 35. Inaddition to the verification through pyrophyllite behavior, knowledge ofseveral other well-known behaviors have been used to verify theparameters and other procedures adopted in the software. Calcite andgypsum unit cells and water molecule are also shown in FIGS. 36, 37, and38.

The simulation study consisted of several steps starting from sorptionof water molecules on the individual crystallite, assemblage ofcrystallites through natural randomness concepts, compaction to themaximum density, relaxation to simulate stress relief, and finallyvolume change upon sorption of water molecules in the pore spaces. Theprocedure is repeated for all the three CEC varied Na-montmorilloniteand further variations in the exchangeable cations and the cementationdue to the interactions with other soil constituents (Tables 10, 11, and12). All the simulations as per combinations in Table 10 were carriedout on Na-montmorillonite with Na as the sole exchangeable cation. MCECNa-montmorillonite was then selected to simulate the cementation effectsdue to potassium chloride, gypsum, and calcite as per permutations inTable 11. LCEC montmorillonite was finally selected for the simulationsby changing the type and amount of exchangeable cations as given inTable 12.

TABLE 10 Summary of various variations and combinations used insimulations for Na-montmorillonite (Na as 100% exchangeable cation). CECMoisture (meq/100 g) Designation Density conditions* conditions 54 LCECStress relieved at 1000 kPa 10, 20, 30, and 40% 90 MCEC Stress relievedat 1000 kPa 10, 20, 30, and 40% 144  HCED Stress relieved at 1000 kPa10, 20, 30, and 40% *compacted at 1, 0.1, and 0.01 GPa

TABLE 11 Simulation permutations of cementation agents for MCECNa-montmorillonite. Cementation Moisture Agent Percentage Densityconditions conditions Gypsum Max 20 Stress relieved at 1000 kPa 10 and30% (CaSO₄, 2H₂O) Calcite (CaCO₃) Max 10 Stress relieved at 1000 kPa 10%Potassium Max 10 Stress relieved at 1000 kPa 10% Chloride (KCl)

TABLE 12 Simulation permutations for various combinations ofexchangeable cations for LCEC montmorillonite. Exchangeable CationsCombinations Na⁺ K⁺ Mg⁺² Ca⁺² 1 40 60 — — 2 40 — 60 — 3 40 — — 60 4 4020 40 — 5 40 20 — 40 6 40 20 20 20

The detailed procedures involved in all these steps for a typicalcomplete case for MCEC (90 meq/100 g) montmorillonite and one case ofchange in exchangeable cations in LCEC (54 meq/100 g) montmorilloniteare provided below, with the molecular simulation results shown by FIGS.210 to 226.

The water sorption step simulates the sorption of water molecules on theindividual Na-montmorillonite crystallites. It represents the processesof water mixing with the clay in the laboratory conditions or theinteraction of clay particles with water during the geologicaldepositional processes. Based on the knowledge from the literature andthe findings of XRD results of the samples with similar densities on themoisture density plots in the present disclosure, a basic crystallitesize of a×b×c: 26×54×20 Å was chosen as the fundamentalparticle/crystallite for Na-montmorillonite in the simulation.

Water molecules sorption on the individual montmorillonite crystalliteswere simulated using Sorption and Forcite modules of Materials Studiosoftware. Sorption module is based on Monte Carlo simulation techniquein which water molecules get sorbed on the clay particle on itssurfaces, interlayer, and edges. In Sorption module, sorbate (singlewater molecules) is absorbed in the sorbent framework of clay molecule.Fixed loading was used to find the global minimum energy sites for thewater molecules in a clay crystallite by running cycles of fixed loadingsimulation series where the temperature is steadily reduced over theseries. Metropolis Monte Carlo method (Metropolis et al.) used in theSorption module is a conventional Monte Carlo method in which trialconfigurations are generated without bias. See Metropolis, N.;Rosenbluth, A. W.; Rosenbluth, M. N.; Teller, A. H.; Teller, E. J.(1953), “cccc” Chem. Phys., 21, 1087, incorported herein by reference inits entirety. This method was selected for the simulations as it treatsthe sorbate structure as rigid and only rigid body translations andreorientations are incorporated. In the sorption module, ratios forexchange, conformer, rotate, translate, and regrow have been selected as0.39, 0.2, 0.2, 0.2, 0.2 respectively, while the correspondingprobabilities are 0.39, 0.2, 0.2, 0.2, and 0.2. Amplitudes adopted forrotation and translation are 5° and 1 Å respectively. These selectedparameters in Monte Carlo simulations have been verified through thefindings and results of certain well known baseline facts. Facts such asformation of 3 Å thick water layers upon absorption of about 10% waterand hydration radius of sodium cation have been used in the verificationof the choice of the parameters.

The simulation is based on the concept of finding locations in the unitcell where water molecules would cause the maximum lowering in theenergy. The water molecules get to the locations in the unit cell basedon the lowering of the energy principle and the sorption is continuedtill an energy cut off is reached. After experimenting several energycut off levels, 25000 steps cut off was adopted as the threshold limitfor the realistic sorption. Simulation beyond 25000 steps resulted inthe occupation of higher energy sites by water molecules and anunrealistically high volume change occurred. Moreover, pyrophyllite wasalso shown to be adsorbing water and showing high swell potential atsteps more than 25000. After sorption of the water molecules in 25000steps, equilibration was achieved in 15000 steps to a temperature of298° K. Universal forcefield, one of the built in forcefield in thesoftware was modified and used in the simulation and using the currentcharges associated with the molecules. Ewald summation method wasadopted for the electrostatic forces, while atom based summation wasused for van der Waals forces with cubic spline cut off at 12.5 Å. Thefinal result of the Sorption simulation was a lowest energy frame withthe water molecules sorbed at the most desired locations of the unitcrystallite of montmorillonite; a typical sorption result is shown inFIGS. 39 and 40.

After performing each sorption cut off, the unit crystallite with watersorbed molecules was stabilized through molecular dynamics simulation.Forcite module of the Materials Studio software was used for thepurpose. In Forcite, NPT (constant number of particles, pressure, andtemperature) ensemble was used and simulations were performed usingmodified Universal forcefield for a period of 5 to 30 ps in 0.5 fsintervals or till a constant volume is achieved. Berendsen thermostatwith a decay constant of 0.1 ps was used to control the temperatureduring the simulation. During the molecular dynamics simulation,temperature was kept constant at 298° K. Simulations were carried out atatmospheric pressure (100 kPa) and Berendsen barostat with decayconstant of 0.1 ps was used to control the pressure of the system.Berendsen methodology was found as the most suitable for the singlecrystallites after several trials with other thermostats and barostatsavailable in the software. A typical post molecular dynamics molecule isshown in FIGS. 39 and 40.

As evident from FIGS. 39 and 40, water molecules are getting sorbed onthe surface, edges, and the interlayer of the montmorillonitecrystallite. The water sorbed in the interlayer causes the latticeexpansion. The entire process of sorption and dynamics is repeated andthe lattice expansion is noted with each increase in water content. Atotal of 277 water molecules sorption is equivalent to 10% water contentof the unit crystallite of montmorillonite of 26×54×20 Å size. Thesimulation was continued to a maximum water content of 40%. Latticeexpansion (d-spacing) for MCEC Na-montmorillonite is plotted againstsorbed water content in FIG. 41. Change in lattice spacing with moisturecontent of the loose bentonite as determined through XRD is also plottedin FIG. 41. The verification of sorption parameters has been carried outusing the pyrophyllite crystallite of the same size asNa-montmorillonite as described herein later. These water sorbedcrystallites were then used to model the loose soil mix using naturalrandomness process through Monte Carlo simulation.

Pyrophyllite is the clay mineral in which no isomorphous substitutiontakes place and hence its CEC is zero. In order to verify thecombination of parameters being used for the sorption of the watermolecules in a montmorillonite crystallite, pyrophyllite crystallite ofthe same size (54×26×20 Å) was also used for the simulation. Adoptingthe same parameters in the sorption simulation, pyrophyllite did notshow any adsorption of the water molecules.

So parameters selected for sorption module got further calibration andverification through this process.

Sorption module was used to simulate the assemblages of water sorbedcrystallites when mixed together in the loose form before the compactionprocess. For the purpose, four crystallites were randomly sorbed in a125×125×125 Å cubic unit cell (FIGS. 42 and 43). Several cubic unitcells sizes ranging from 100 Å to 200 Å were experimented and 125 Å wasfinally selected. Bigger unit cells resulted in distances larger thanthe crystallite themselves and smaller ones caused overlapping of thecrystallites. Based on the randomness analogy and the parameters used inthe Monte Carlo simulation in Sorption module for the singlecrystallite, these four crystallites occupy relative positions in thecubic space (FIGS. 42 and 43). The relative positions are taken up bythe crystallites either parallel to faces, edge to edge, edge to theface, or an intermediate form depending on the charge distribution oneach crystallite and the moisture content. These unit cells repeatinfinitely in space with the superposition of the periodic boundaryconditions. In this way, several possible fabrics during the loose mixstate were created using Sorption module of the software. As a nextstep, simulation of the creation of the fabric and structure due tocompaction was performed using molecular dynamics Forcite module asdetailed below.

To simulate the fabric and structure in the compacted specimens, unitcells consisting of the loose clay crystallites created in the previousstep were compressed to the required density using Forcite moleculardynamics module. NPT ensemble was used to compress the unit cell to highdensity at different confining pressures of 0.01, 0.1, and 1 GPa.Different confining pressures were used to simulate the several levelsof geological and laboratory compaction pressures. A comparison of themaximum density achievement at different pressures is shown in FIG. 44.The simulations were run to 30 ps or more at an interval of 0.5 fs toachieve the maximum density. In this simulation, Berendsen thermostatwas used as in Sorption module, while Berendsen barostat was replaced byParrinello barostat. As Berendsen barostat applies pressure in all thedirections in such a way to keep the unit cell dimensions equal, thecorresponding reduction of volume on all the faces of the periodicboundary cell remains uniform. Thus, Berendsen barostat does notsimulate the real compaction process in which stresses vary along thefaces under a uniform pressure compaction process. The dynamicscompaction simulation was continued until a maximum density is achieved.A 3-D view of several combined unit cells in FIG. 45 provide a clearvisualization of the created fabric. The compacted unit cell and thecorresponding compaction curve is shown in FIGS. 46 and 47.

To simulate the overconsolidation process by the removal of geologicaloverburden, next step in the simulation process was the relaxation ofthe compacted structure at low confining pressure and is detailed below.

Expansive day deposits present at shallow subsurface level have suffereda stress relief due to removal of high geological pressures initiallyresponsible for the creation of highly compacted soil structure. Thisprocess causes overconsolidation in the compacted expansive clay layers.To simulate the process of overconsolidation on the compacted unit cell,dynamics through Forcite module of the software was used at a confiningpressure of 0.001 GPa. Due to a representative overconsolidationpressure in most of the expansive clay deposits in the area, a confiningpressure of 0.001 GPa has been selected as the confining pressure forthe relaxation simulation. The relaxed structure of the unit cell afterthe dynamics simulation and the corresponding relaxation curve is shownin FIGS. 48 and 49. The stress relaxed unit cell is now ready to besimulated for the water intake and the corresponding simulation of theswell/volume change behavior. The details of water sorption in the poresof the unit cell and the volume change behavior simulation is providedbelow.

The stress relaxed unit cell was sorbed with water molecules in theintra and interlayer of the crystallites/particles using sorption moduleof the software. A maximum number of 25000 steps for the sorption ofwater molecules were used to apply the energy cutoff. FIG. 50 shows thesorbed water molecules in the stress relaxed cell.

Upon the completion of sorption step, dynamics was performed on thewater sorbed unit cell. The dynamics was continued until a stabilizedvolume/density is obtained. The unit cell after the volume changeprocess simulated through dynamics and the corresponding volume changecurve are shown in FIGS. 51 and 52.

The process of water molecules sorption and the subsequent dynamicsleading to a stabilized volume was repeated until a dry density of 0.5g/cm³ was obtained. A dry density of 0.5 g/cm³ is considered a terminalpoint for the swelling process. Equivalently, this can also bedetermined once cohesive energy density of 6×10⁸ J/m³ is reached duringthe dynamics simulation process. In the present disclosure, cohesiveenergy density concept is applied to the behavior of expansive clays andhas been used for the volume change model formulation. Volume changeversus water content curve for MCEC Na-montmorillonite with initialmoisture content of 30% is shown in FIG. 53.

In addition to the simulations with Na-montmorillonite, simulations werealso carried out using other inclusions resulting in thecementation/cohesion effects. The simulations considering thesevariations are discussed below.

In addition to the presence of non-clay inclusions in the expansive claydeposits as an inert materials, gypsum, calcite, and other salts arealso responsible for the cementation/cohesion among the clay particles.In order to simulate this process, individual atoms/molecules such asCa²⁺, SO₄ ²⁻, K⁺, Cl⁻, and CO₃ ²⁻ were sorbed in the water bearingmontmorillonite crystallites. For the purpose, 10% water was sorbed ontothe montmorillonite crystallite with a CEC of 90 meq/100 g. Sorption of10% water was performed in order to create a media in which otherminerals can get dissolved. To simulate the dissolution of gypsum in thesorbed water layer, Ca²⁺ and SO₄ ²⁻ were sorbed in and around thecrystallite using Sorption module of the software. About 20% Gypsum wasadded to the clay crystallite, creating an envelope of Ca²⁺ and SO₄ ²⁻around the molecule (FIGS. 54 and 55).

Similarly to simulate the adsorption of potassium chloride and calcitein the sorbed water of clay crystallite, K⁺/Cl⁻ and Ca²⁺/CO₃ ²⁻ wererespectively sorbed using the Sorption module of the software. Theseprocesses led to the formulation of the individual crystallitescontaining the respective molecules.

Rest of the procedure including the simulation of loose mix ofcrystallites, compaction, stress relief, water sorption, and theswelling is same as described above for the MCEC Na-montmorillonite. Thefinal unit cell after swelling simulation for the Gypsum sorbed case isshown in FIGS. 54 and 55. A swell cutoff selected for these cases is thequantity of water adsorbed in any single step. Water sorption as low as2.0 to 4.0% is indicative of extremely small size of pores and thecorresponding extremely low permeability. Therefore, such low values ofwater adsorption are practically not possible in such highlydensified/cemented mass of expansive clay structure. Rest of thesimulation results using potassium chloride and calcite are shown inFIGS. 210 to 226.

All the above simulations were carried out using montmorillonite havingsodium as the only exchangeable cation. To study the influence ofvarying types and proportions of the exchangeable cations, LCECmontmorillonite was subjected to changes in the types and numbers ofexchangeable cations. For this purpose, Na⁺ cations in LCECmontmorillonite were partially replaced with K⁺, Mg²⁺, and Ca²⁺ cationsas per the permutations in Table 12. Rest of the process followed forsuch cases was the same as adopted for MCEC Na-montmorillonite describedearlier. The results for various exchangeable cations combinations bymolecular simulation are shown by FIGS. 210 to 226.

The concepts of cohesive energy and cohesive energy density were firstintroduced into the theoretical treatment of mixtures by Hildebrand(1916, 1919, 1933, 1970) and Scatchard (1931). See Hildebrand, J. H.(1916), “Solubility”, J. Am. Chem. Soc., 38, 1452; Hildebrand, J. H.(1919), “Solubility III. Relative Values of Internal Pressures and theirPractical Application”, J. Am. Chem. Soc., 41, 1067; Hildebrand, J. H.,Scott, R. L. (1933), “Solubility of Non-Electrolytes”, 3rd Edition,Reinhold: New York; Hildebrand, J. H., Prausnitz, J. M., and Scott, R.L. (1970), “Regular and Related Solutions”, van Nostrand: New York;Scatchard, G. (1931), “Equilibria in Non-Electrolyte Solutions inRelation to the Vapor Pressures and Densities of the Components”, Chem.Rev., 8, 321, each incorporated herein by reference in their entirety.In their theories, the cohesive energy is used to estimate the energychange on mixing two species. When supplemented with the entropy ofmixing it allows the prediction of the phase behavior of simplemixtures.

The cohesive energy density concept is used first time in the presentdisclosure in relating the swelling behavior of expansive clay mineralsto the various variants such as moisture, density, CEC, type, andproportion of exchangeable and total cations etc. Cohesive energy isindicative of how strongly the molecules/crystallites are coherent witheach other due to the inherent CEC or cementation effects. The higherthe cohesive energy density of the expansive clay structure, the lesserthe swelling potential of the clay minerals. A swell cutoff selected forthese cases is the quantity of water adsorbed in any single step. Watersorption as low as 2.0 to 4.0% is indicative of extremely small size ofpores and the corresponding extremely low permeability. Therefore, suchlow values of water adsorption are practically not possible in suchhighly densified/cemented mass of expansive clay structure. Moreover,swell cutoff for these cases also derives from the fact that swell willtake place for the cohesive energy density corresponding to its originalcounterpart (without cementation and with Na cations only). Using theseboth concepts, swell potential was evaluated for these cases.

Cohesive energy density was measured for all the simulation cases usingForcite module of the software. Total cohesive energy density wasplotted against the moisture content for all the steps in eachsimulation case as loose mix, compaction, relaxation, andswelling/volume change with water. Typical variation of cohesive energydensity for HCEC, MCEC, and LCEC Na-montmorillonite are shown in FIGS.56, 57, and 58. See also FIGS. 210 to 226.

Forcefield plays a vital role in any molecular simulations study. Itprovides the relative interaction among the particles by defining theenergy relationship for the system. Usually, in studies involved in thesimulations of clay minerals, CLAYFF forcefield (Cygan et al.) and someothers specifically prepared for the purpose have extensively been used.

But all of these have been applied exclusively for a single clay unitmolecule cell. For the scenarios of several crystallites in a unit cellas used in the present disclosure, these forcefields have limitationsespecially when the unit cells/single crystallites are converted tonon-periodic superstructure for sorption purpose. Universal forcefield(UFF), the forcefield embedded in the software, consists of universalparameters to cover the entire periodic table and may be used for suchscenarios. When UFF was applied to several scenarios formulated in thepresent disclosure, several well-known facts could not be verified.Therefore, it was planned to do changes and modifications to the UFF asper the requirements of a typical forcefield applicable to clay mineralsinteraction with water. So, several forcefield parameters in UFF weremodified in the light of the parameters suggested in CLAYFF forcefield.The parameters for Na, Ca, Mg, Al, and Si were accordingly modified. Theoriginal and the corresponding modified parts of the UniversalForcefield (Original and Modified Universal Forcefields (UFF)) are shownbelow, while the comparison of the results of typical swell ofNa-montmorillonite crystallite using the original and modified UFFs areshown in FIG. 59.

Original Universal Forcefield Atom Types Na Na 22.99000 0 0 0 0! sodiumMg3 + 2 Mg 24.31000 0 3 0 0! magnesium, tetrahedral, +2 oxidation stateAl3 Al 26.98150 0 3 0 0! aluminium, tetrahedral Si3 Si 28.08600 0 3 0 0! silicon, tetrahedral K_ K 39.94800 0 0 0 0! potassium Ca6 + 2 Ca40.08000 0 6 0 0! calcium, octahedral, +2 oxidation state

Diagonal vdw Na LJ_6_12 2.9830 0.3000E−01 Mg3 + 2 LJ_6_12 3.02100.1110E+00 Al3 LJ_6_12 4.4990 0.5050E+00 Si3 LJ_6_12 4.2950 0.4020E+00K_ LJ_6_12 3.8120 0.3500E−01 Ca6 + 2 LJ_6_12 3.3990 0.2380E−00

Atom typing rules Mg3 + 2 Mg 0 0 0 1 Al3 Al 3 0 0 1 Si3 Si 3 0 0 1

Generators Na 1.5390 180.0000 1.0809 0.0000 0.0000 0.0000 3 −1 0.00002.84300 Mg3 + 2 1.4210 109.4712 1.7866 0.0000 0.0000 0.0000 3 −1 0.00003.95100 Al3 1.2440 109.4712 1.7924 0.0000 0.0000 0.0000 3 −1 0.00003.04100 Si3 1.1170 109.4712 2.3232 0.0000 0.0000 0.0000 3 −1 1.22504.16800

Modified Universal Forcefield Atom Types Na Na 22.99000 0.0000 0 0 0 !sodium Mg6 + 2 Mg 24.31000 0.0000 6 0 0 ! magnesium, octahedral, +2oxidation state Al6 Al 26.98150 0.0000 6 0 0 ! aluminium, octahedral Si3Si 28.08600 0.0000 3 0 0 ! silicon, tetrahedral K_ K 39.94800 0.0000 0 00 ! potassium Ca6 + 2 Ca 40.08000 0.0000 6 0 0 ! calcium, octahedral, +2oxidation state

Diagonal vdw Na LJ_6_12 2.6378 0.1301E+00 Mg6 + 2 LJ_6_12 5.90900.9029E−06 Al6 LJ_6_12 4.7943 0.1329E−05 Si3 LJ_6_12 3.7064 0.1841E−05K_ LJ_6_12 3.7423 0.1000E+00 Ca6 + 2 LJ_6_12 3.3990 0.2380E+00

Atom typing rules Mg6 + 2 Mg 0 0 0 1 Al6 Al 3 0 0 1 Si3 Si 3 0 0 1

Generators Na 1.5390 180.0000 1.0809 0.0000 0.0000 0.0000 3 −1 0.00002.84300 Mg6 + 2 1.4210 109.4712 1.7866 0.0000 0.0000 0.0000 3 −1 0.00003.95100 Al6 1.2440 109.4712 1.7924 0.0000 0.0000 0.0000 3 −1 0.00003.04100 Si3 1.1170 109.4712 2.3232 0.0000 0.0000 0.0000 3 −1 1.22504.16800

In the above Universal forcefields, “tetrahedral” and “octahedral” under“Atom Types” refer to the hybridization state or geometry. Diagonal vdwrefers to diagonal Van der Waals interactions represented with theconventional 12-6 Lennard-Jones function that includes the short rangerepulsion and the attractive dispersion energy. “Atom typing rules”refer to the rules that define the element, hybridization, connectionsto other atoms, and ring membership that are characteristic for eachatom type. “Generators” are parameter generators that calculateforcefield parameters by combining atomic parameters. The atomicparameters are combined using a prescribed set of equations (rules) thatgenerate forcefield parameters for bond, angle, torsion, inversion(i.e., out-of-plane), and van der Waals and Coulombic energy terms.

This disclosure includes three major activities: macro level testing,micro level imaging and analysis, and molecular level simulation andmodeling. These activities have led to the formulation of a volumechange behavior model for the molecular/nano level structure ofexpansive clayey soils. The nano level model can be coupled with microand macro level models to formulate a comprehensive volume change modelfor the expansive soils. The macro level behavior of the expansive soilshave been studied through the free swell potential tests on variouscombinations of clay and non-clay minerals, undisturbed natural samples,compacted at various moisture and density conditions (Table 8). Freeswell tests results tabulated in Table 9 and plotted in FIG. 32 revealthat there is a general increase in swell potential with increase inbentonite content, rate of increase in swelling is reduced as bentonitecontent increases to the maximum value of 100%. This decrease in rate ofswell could be attributed to the reduced permeability or water intakecapacity of the fabric of the compacted clay and sand mixes. As theswelling increases, more swollen particles start occupying the biggerpores, thus further impeding the water flow rate in the clay fabric.This fact can be qualitatively confirmed through the ESEM results of thetypical fabrics of sand-bentonite mixes in FIGS. 60 and 61. This figurereveals very small size of pores for the 100% bentonite case while arelatively open fabric containing relatively large sized pores in caseof higher percentages of sand. Based on the above facts, the aspect ofpermeability of the fabric should have a special consideration besidesdensity, in the modeling of total swell potential of closed fabricscomposed otherwise of high swell potential clay minerals. Relativelylower permeability may not allow the permeation of enough water requiredfor the complete swelling of all the clay mineral particles present inthe soil fabric. This phenomenon needs to be translated into asignificant factor in the volume change modeling of the expansive clays.Permeability characteristics of the micro fabric should also be coupledwith the macro fabric features such as fissures and stress cracks todefine the water intake potential of the entire structure of theexpansive clayey soils.

Use of static compaction to prepare the samples with the same densityachieved through dynamic Proctor compaction has led to an equivalentstatic pressure of 1500 kPa. As the fabric created using the staticcompaction is less dispersed in nature (agglomerates are obvious in FIG.189), it has resulted in higher swelling (121%) than it's dynamically(Proctor) compacted counterpart (89%). Although kaolinite is anon-expansive clay mineral, replacing sand partly with kaoliniteresulted in reduced swelling (95%) as compared to the one with noreplacement. This phenomenon may again be attributed to the lowpermeability of the fabric containing high percentage of fine grainedkaolinite replacing part of coarse grained sand.

Referring to Table 9, replacing part of the sand by calcite and gypsumhas resulted in substantial reduction in swelling of the bentonite/sandsamples. There is a reduction of 82%, 90%, and 95% in the swellingpotential when gypsum was added at 10%, 30%, and 50% to replace thesand, respectively. Similarly, there is a reduction of 40% and 44% inswelling upon part of the sand being replaced by 30% and 50% calcite,respectively. The phenomenon of decrease in swelling by addition ofcalcite and gypsum might be resulting from the binding effects producedby these compounds to the individual or group of clay particles. Ascalcite and gypsum in their powdered form were mixed with bentonite andwater, these minerals get dissolved in the molding water to varyingdegree of dissolution. The resulting cations and anions dissolved inwater get adsorbed on the surface and interlayer of the clay particles.This phenomenon provides additional binding forces to the individual andgroup of clay particles. As solubility of powdered gypsum in water isgenerally higher than calcite, it is causing more reduction in theswelling when added in equivalent quantities. This theory of theadditional binding effects or cohesion provided by these compounds canbe visualized through ESEM results in FIGS. 191 and 192 for gypsum andFIGS. 199 and 200 for calcite, respectively. These figures clearly showthe closed fabrics due to additional bonding or cohesion created as aresult of the presence of these compounds. As it is difficult tovisualize the dissolved salts causing cohesion to the clay particles,this bonding/cohesion theory was further verified through molecularlevel simulations.

Presence of bonding/cohesion can also be imagined from the fact thatalthough the CEC and the percentage of smectite in the naturalundisturbed sample of Qatif-1 is almost same as those of the commercialbentonite (30/70 sand-bentonite mix), the difference in percent swell islarge, i.e., 29% vs. 121% This difference may be attributed to thecementation effects provided by the calcite, gypsum, and other similarcompounds or salts present in the soil. To further investigate theseresults, in addition to the exchangeable cations, total cations werealso determined for the bentonite and undisturbed samples. The reasoningprovided above for the various phenomena responsible for the macro levelbehavior were further confirmed through micro level investigations. Someof the interpretations were confirmed through direct imaging techniquesand other through the analysis of the data and results of these tests.The results acquired through these tests and the correspondingdiscussions and explanations are provided below.

X-Ray Diffraction (XRD) test is primarily used for the mineralogicalanalysis of crystalline samples. In the present disclosure, XRD has notonly been used for the determination of the mineralogical composition ofthe laboratory compacted specimens and the undisturbed samples obtainedfrom the natural deposits, but also for the study of change in latticed-spacing in crystal lattice of clay mineral with water content. Changein d-spacing in the clay mineral structure was determined both on thespecimens from the loose mix and the compacted samples.

Loose mixture of bentonite samples were prepared by mixing the soil withdifferent water contents ranging from 10 to 100%. XRD tests wereperformed on each of these samples and the resultant d-spacing as afunction of water content is shown in FIG. 41, which is evident thatthere is an increase in lattice spacing with water content to a spacingof 17.5 Å at 60% water content and remains constant afterwards to awater content of 100%. As d-spacing of dry bentonite is 10 Å and eachwater layer occupies an approximate thickness of about 2.5 Å in theinterlayer space, 17.5 Å indicates the presence of three water moleculeslayers in interlayer. Each water layer of about 2.5 Å in the interlayerconstitutes about 10% water content. This indicates that the maximumwater content accommodated in the interlayer space in clay minerals isabout 30% and the rest of the water is adsorbed on the ends and edges ofthe clay mineral crystallites. This fact constitutes a significantaspect in the molecular level simulation and modeling.

In addition to the XRD tests on the specimens from the loose mixture atvarious water contents, these tests were also conducted on the samplescompacted on the dry and wet side of OMC. FIGS. 62, 63, 64, and 65indicate that d-spacing of about 15 Å (equivalent to two water layers or20% water content) exists in the clay crystallites on the dry side ofOMC while d-spacing of 17.5 Å occurs (equivalent to three water layersor 30% water content) on wet side of OMC. As the molding water contentis respectively 30 and 40% for the dry and wet side of OMC, it isestablished that rest of the 10% water content for both the cases isadsorbed on the edges and ends of the crystallites. This fact has playeda key role in the assessment of the fundamental size of the crystallitein the molecular level simulation.

Fundamental crystallite size was also assessed from the XRD data usingDebye-Sherrer's method (Sherrer). See Scherrer, P. (1918), “Bestimmungder Grösse and der inneren Struktur von Kolloidteilchen mittelsRöntgenstrahlen” Nachr. Ges. Wiss. Göttingen 26 (1918) pp. 98-100,incorporated herein by reference in its entirety. The mechanism based onthe concept of inverse relationship between width of an X-Raydiffraction peak and the crystallite size is shown in FIG. 33. Using theFull Width at Half Maximum (FWHM) of the corresponding peaks in the XRDdata, removal of background to obtain the net peak intensity haveresulted in the assessment of the crystallite size in the range of 59 to108 Å. This knowledge has been used in the selection of the size of thecrystallite in molecular level modeling.

Environmental Scanning Electron Microscopy (ESEM) results have provideda clear conception of several features of the fabric of the pre and postswell samples. For the samples with 100% A bentonite, particles haveshown greater spacing in the post swell state (FIG. 172), while the oneshaving other minerals such as calcite and gypsum have shown closedfabric of the nano clay particles in the microstructure. These twofeatures support several explanations regarding the specific behaviorobserved during the swell potential tests. For example, high swelling of100% bentonite samples and highly reduced swelling for the samplescontaining gypsum or calcite.

Energy Dispersive Spectroscopy (EDS) was performed both on specific areaor focused points of the specimens during the performance of ESEM. EDSresults indicate the presence of Na⁺ and Ca²⁺ as two major cations inthe bentonite. From the FIGS. 175 to 178, it can be observed thatalthough intensity of peak for Na⁺ cations is present both in pre andpost swell samples. Ca²⁺ peak is present in pre swell samples only andit diminishes in the post swell samples. Based on this observation, itcould be inferred that not all the Ca²⁺ cations may be exchangeable innature, rather most of these may be associated with clay crystallites asnon-exchangeable cations. These non-associated Ca²⁺ cations aftergetting dissolved in water might have drained away in the free water andthus not appearing the EDS results of post swell samples.

In case of samples containing sand and other non-clay inclusions, clayparticles have found to be coating the bigger non-clay particles. Forthe samples containing gypsum, ESEM in FIGS. 191 and 192 reveal the claylayers to be present as cohesive assemblages. On the other hand, basedon the ESEM results of the samples containing Calcite (FIGS. 199 and200), calcite has been found in crystal form on the specimens. Fromthese results, relatively higher dissolution of gypsum in water ascompared to calcite may be inferred.

Fourier Transform Infrared Spectroscopy (FTIR) has been extensively usedfor the investigations of the molecular level behavior contributing tothe macro behavior of the expansive clays (Katti and Katti, 2010). SeeKatti, K. S. and Katti, D. R. (2010), “Fourier Transform InfraredSpectroscopy Studies of Clay and Shales”, Indian GeotechnicalConference—2010, GEOtrendz, Dec. 16-18, 2010, 267-270, incorporatedherein by reference in its entirety. In case of clays interacting withwater, H—O—H bending vibration and O—H stretching vibration bandsprovide the vital information on the level of interactions at variousinterlayer water contents. Both the vibration bands under stable/dryform are 1694 cm⁻¹ and 3634 cm⁻¹, respectively (Katti and Katti, 2010).When water enters the interlayer of the clay crystallites, H—O—H bendingband shifts to lower energy levels depending on the water content. InFIG. 146, it can be noticed that there is a reduction in H—O—H bendingband from 1694 to 1650 cm⁻¹ in bentonite loose mixed samples withmoisture content from 40 to 60% and remains same at higher moisturecontents. This confirms the trend as observed in the XRD analysis of thebentonite samples mixed with varying percentages of water. Moreover, O—Hstretching band achieves higher energy from 3634 to 3650 cm-1 as aresult of the addition of water. A similar trend of reduction in theH—O—H bending band and O—H stretching band have been observed in all thepost swell specimens. FTIR have proven to be a complementary techniquefor the investigations of nano level changes in the clay structure dueto the interaction with water.

Presence of non-clay minerals and constituents in any natural orcompacted expansive soils play a vital role towards the total swellpotential. Most of the non-clay minerals such as calcite, gypsum, andother compounds or salts of sodium and potassium exist in cations andanions form when present in pore solution of these deposits. Part of thecations such as Na⁺, K⁺, Ca²⁺, and Mg²⁺ get adsorbed on the surfaces andinterlayer of the charged clay mineral crystallites, while others existeither as isolated fabric or associated with the individual or group ofclay crystallites by covering them on the surfaces, ends, and edges.

During the swell potential testing phase, it was observed that presenceof non-clay minerals such as calcite and gypsum act as swell retarders.It was hypothesized at that stage that these non-clay minerals provide asort of additional binding/cohesion to the individual and group ofexpansive clay particles. To find out a correlation among the type,nature, and quantity of non-clay cations and the swelling potential,both total and exchangeable cations were determined.

Results of the total and exchangeable cations, summarized in Table 5provide an estimate of the non-exchangeable cations present in thesamples. Comparison of the percentage of non-exchangeable cations withthe percent of expansive clay minerals may provide a very close estimateof the swell retardation percent.

Owing to its micron level resolution, Micro Computed Tomography (MicroCT) is limited in its use for the nano/molecular level studies. In thisstudy, micro CT has been used only to visualize and evaluate the micronlevel fabric of the pre and post swell samples using the contrastingattenuation property of the clay particles before and after the swelltest. This concludes that CT could be used as a general tool for theassessment of the factors contributing to the swell potential of anycompacted or natural clay matrix. Micro CT results indicate theagglomeration of the fine grained clay particles in the pre swell statewhile these become more dispersed in their post swell state (FIGS. 203Ato 209B). Conclusion drawn in swell potential tests regarding the swellretardation caused by the non-clay constituents and visualized in ESEMresults are also indicative through CT results. In FIGS. 203A to 209B,pre and post swell CT scans indicating several parts of the specimensshowing no change in attenuation color are indicative of the particleassemblages restrained from swell through cohesion/bonding created bynon-clay constituents such as calcite, gypsum, and other salts presentin soils.

Molecular level modeling and simulations performed in the presentdisclosure are divided into various steps. Molecular level modelingtechniques such as molecular mechanics (MM), molecular dynamics (MD),and Monte Carlo (MC) simulations have been used to study the processesand interactions occurring at the molecular level in the natural andcompacted fabrics of the expansive clayey soils. These simulationtechniques were used to study the interactions between clay and non-clayparticles with various combinations of CEC, interlayer and intra layercations, anions, and water under various fabric and structureconditions. Basic clay mineral was represented by a montmorillonitecrystallite of 54×26×20 Å size.

Cohesive energy density (CED) concept has been used to explain variousmolecular level processes and interactions occurring at different levelsof the volume change in expansive clayey soils. CED has been foundsensitive to all the possible changes in the clay structure due tovariation in CEC, interlayer and intra layer cations, anions, water, anddensity conditions. Total CED of any combination of molecules iscontributed from two components, i.e., electrostatic and van der Waalsforces. Contribution from van der Waals could either be repulsion orattraction in nature, while it is always attraction in nature fromelectrostatic forces. The results of each step are discussed andinterpreted in the light of the CED concept.

The simulation of the sorption of water molecules onto a singlecrystallite of montmorillonite was carried out using Sorption module ofthe software. Each sorption phase consisted of 25.000 steps of MonteCarlo simulation followed by molecular mechanics and dynamics usingForcite module to achieve a stable configuration of the sorbed watermolecules, cations, and the crystallite layers. It is evident from firstsorption phase shown in FIGS. 66 and 67 that water molecules startoccupying the locations next to Na⁺ cations present in the interlayer.This phenomenon reveals that water molecules start hydrating theinterlayer cations in the first instance. Completely hydrated Na⁺ areshown in FIGS. 68 and 69. It was observed in the subsequent phases thatwater molecules start making bonds with the edges, ends, and interlayerto satisfy the crystalline swelling. It is important to observe that notall the water molecules occupy the interlayer, rather these equally getsorbed on the edges and ends of the crystallite. For instance, when thetotal sorbed water content on a single crystallite reaches 20%, latticeexpansion (d-spacing) in FIGS. 39, 40, and 41 reveals only 10% water tobe present in the interlayer. Similarly, this lag continues for the restof the higher moisture contents and the water molecules sorptioncontinues equally on the edges and the interlayer. This fact visualizedin the molecular simulations have also been confirmed through thevariation in lattice d-spacing with moisture content in XRD resultsshown in FIG. 41. Comparison between the lattice expansion in themodeling and the experimental values from XRD are showing an excellentagreement. This phenomenon leads to an important conclusion that claymineral particles might exist in the form of bigger size crystallites ofan order of 1000+A in the dry form, but start breaking up into muchsmaller crystallites once come in contact with water. During thecompaction phase, these smaller crystallites join at the edges and endsto become larger particles with the water present in between the joinedparts. Fabric created after the compaction process is discussed herein.

Based on the previous discussions, the parameters selected in theSorption and Forcite modules including the modified Universal forcefieldare confirmed. A comparison of the swelling results from the originaland the modified Universal forcefields is shown in FIG. 59. Thecomparative plots clearly indicate the disability of the originalUniversal forcefield to predict the real swell behavior of singlemontmorillonite crystallite. Moreover, the concept of using 25,000 stepsas threshold for the water molecules sorption and other parameters inSorption Monte Carlo simulation have also proven to be accurate. Tofurther confirm and verify the parameters and the procedure, sameprocess of water sorption was adopted for the pyrophyllite crystallite.The procedure and parameters further confirms as no water molecule couldbe sorbed in pyrophyllite crystallite of the same size (54×26×20 Å)during the 25,000 steps of Monte Carlo simulation.

General trend and the quantitative change in lattice d-spacing is verysimilar for all the CECs in FIG. 41, but anomalously, LCEC has shown aslightly higher expansion than HCEC and MCEC especially at lower watercontents. Difference is small; however, this anomalous behavior mostprobably owes to the availability of more space in the interlayer ofLCEC due to lesser number of interlayer cations. This allows more watermolecules to wedge in the interlayer and consequently causing a littlehigher expansion in the initial stages of water intake. On the otherhand, amount of water molecules intake in the interlayer of HCEC in theinitial stages is offset by more water intake required for the hydrationof the more number of cations. This results in almost the same latticeexpansion at higher water contents. Another important conclusion drawnfrom this study is that lattice expansion becomes constant to maximum ofthree layers of interlayer water (17.5 Å) after a certain total watercontent (60% in case of this study). Any further increase in watercontent takes place at the edges and ends of the crystallites. Thisphenomenon may be theorized by assuming that the swelling or hydrationforces at this water content becomes smaller enough to cause themovement of the particles against the friction existing in the soil mix.

For the molecules where cations/anions from other compounds such ascalcite, gypsum, and KCl were sorbed, there was a general trend ofsorption both in the interlayer and on the surfaces. Cations ofrelatively small sizes such as Ca²⁺ enters the interlayer while biggeranions such as SO₄ ²⁻, Cl⁻, and CO₃ ²⁻ remain enveloping the surface(FIGS. 70 and 71).

To simulate the effects of presence of the generally available non-swellparticles in the expansive soils, calcite, gypsum, and potassiumchloride molecules were formulated. These molecules were then sorbedonto a single Na-montmorillonite crystallite at different watercontents. The montmorillonite crystallite with previously sorbed watermolecules was further sorbed with equal number of cations and anionsfrom these minerals as shown in FIGS. 70 and 71. Referring to FIGS. 70and 71, the Ca²⁺ cations got sorbed to some extent in the interlayerwhile the rest of Ca²⁺ cations and the anions got sorbed around thecrystallite surface. This scenario could be considered as closelyrepresentative of the generally imagined cementation effects produced bythese particles in any soil mix. These non-swelling minerals sorbedcrystallites were further used to create the compacted mass followed bythe water sorption and the subsequent swelling simulation.

It is rare in nature to find montmorillonite with Na⁺ as the soleexchangeable cation, rather a combination of Na⁺, K⁺, Ca²⁺, and Mg²⁺exist naturally with at least one of these as the predominantexchangeable cation. Basic montmorillonite crystallite was transformedinto various combinations of exchangeable cations as per Table 12.Sorption of water molecules was performed on these combinations in asimilar way as was done for Na-montmorillonite (FIGS. 72 and 73). It wasobserved that general behavior of water molecules sorption was the samefor these crystallites with multiple exchangeable cations. However, someangular shift of the crystallite in space was observed in case ofmultiple cations. This phenomenon most probably owes to the presence ofexchangeable cations of different charges, sizes, and hydration radiiand positioned at random locations in the interlayer. These cationswhile getting hydrated might generate different level of forces in thecrystallite interlayer space and consequently cause an angular shift inthe crystallite position in space.

Sorption module was used to simulate the assemblages of water sorbedcrystallites when mixed together in the loose form before the compactionprocess. For the purpose, four crystallites were randomly sorbed in a125×125×125 Å cubic unit cell (FIG. 43). Several cubic unit cells sizesranging from 100 Å to 200 Å were experimented and 125 Å was finallyselected. Bigger unit cells resulted in distances larger than thecrystallite themselves and smaller ones caused overlapping of thecrystallites. Based on the randomness analogy and the parameters used inthe Monte Carlo simulation in Sorption module for the singlecrystallite, these four crystallites occupy relative positions in thecubic space (FIGS. 42 and 43). The relative positions are taken up bythe crystallites either parallel to faces, edge to edge, edge to theface, or an intermediate form depending on the charge distribution oneach crystallite and the moisture content. Typical fabric formation inloose mix form are shown in FIGS. 74 and 75. It could be noted thatcrystallite arrangement at lower water contents is more random andgenerally follows the face to edge/end configuration, while it becomesmore oriented and adopts parallel configuration at higher watercontents.

In the present disclosure, CED have been considered as a good indicatorof the interaction of the soil structure to the water sorption and theconsequent volume change. Simulated loose mixes of the soil weredetermined through the Forcite module of the software and plotted in thecorresponding graphs in FIGS. 76 to 81. Total CED of the loose mixesvaries from 1×10⁸ to 8×10⁸ J/m³. A general trend observed is that lowCEC crystallites produce lesser cohesive energy while higher CEC and thecrystallites sorbed with other compounds showed higher numbers.

To simulate the fabric and structure in the compacted specimens, unitcells consisting of the loose clay crystallites created in the previousstep were compressed to the required density using Forcite moleculardynamics module. There are several barostats provided in the softwarefor the control of applied pressure on the unit cell; Berendsen andParrinello are two that could be considered suitable for the compactionsimulation of naturally or manually compacted soil samples. In thecompaction simulation, Berendsen thermostat was used as in thesimulation of single crystallite, while Berendsen barostat was replacedby Parrinello barostat. As Berendsen barostat applies pressure in allthe directions in a way to keep the unit cell dimensions equal, thecorresponding reduction of volume on all the faces of the periodicboundary cell remains uniform. Therefore Berendsen barostat does notsimulate the real compaction process in which stresses vary along thefaces under a uniform compaction pressure process. A comparison of thecompressed/compacted unit cells using Berendsen and Parrinello is shownin FIGS. 82 and 83. On the other hand, using Parrinello barostat hasresulted in more realistic way of compaction by varying the stresses onthe faces depending on the shear stresses generated in the unit cell.The resulting fabric is also more random and face to edge fabric onlower moisture content while more oriented and parallel fabric iscreated on higher moisture contents. The variation in relativepositioning or configurations of the crystallites with water content isa well-established fact in compacted clays. FIG. 45 provides a 3-D viewof the repetition of the unit cell in three dimensions in space. Therepetition of unit cell provides the continuity of the crystallites toform soil particles. Since formulation of compactedcrystallites/particles resemble the actual fabrics schematicallyvisualized, it further confirms the selected parameters and proceduresfor the formulation and simulation of compacted fabric of soilparticles.

Different confining or compaction pressures were used to simulate theseveral levels of geological and laboratory compaction pressures.Different pressures have resulted in different maximum densities of theunit cells (FIG. 44). It is evident from FIG. 44, high pressures of anorder of 1 GPa causes quick compaction and may be closely representativeof dynamic and static quick type of compaction using the laboratory andfield equipment. On the other hand, low confining pressures of an orderof 0.01 to 0.1 GPa result in slow compaction and hence may be simulatingmore closely slow compaction f consolidation pressures for thegeological deposits. It could be noted from the plots that densities arealso closely representative of the general range of field and laboratorydensities.

Both total and van der Waals CED for each of the case were determinedusing Forcite module. Total cohesive energy density is plotted in therespective plots (FIGS. 76 to 81), while both total and van der Waalscohesive energy density are tabulated in Table 13. From the plots, itcould be inferred that total CED for any compacted mix is sensitive toall the parameters being considered such as water content, density, CEC,cementation, and type and percentages of exchangeable and total cations.

From Table 13 and FIGS. 76 to 83, total CED has been found to beincreasing with increase in CEC, density, cementation, and bivalentcations and decreasing with water content, while van der Waals cohesiveenergy density reduces and becomes repulsion in nature with the samevariation of the above parameters.

TABLE 13 Summary of swell potential results for all the simulation casesMaximum density Relaxed density van der van der Total Waals Total WaalsInitial cohesive cohesive cohesive cohesive Final Maximum RelaxedTerminal water energy energy energy energy water density density densityCase content density density density density content (g/cm³) (g/cm³)(g/cm³) Swell no Case (%) (J/cm³) (J/cm³) (J/cm³) (J/cm³) (%) Wet DryWet Dry Wet Dry (%)  1 HCEC Na100 — 10 6636 −145 5890 −98 68 2.432 2.2112.132 1.938 0.571 0.340 470  2 20 5379 −80 4500 −33 87 2.112 1.760 1.7621.468 0.617 0.330 345  3 30 4360 −35 3250 2 105 1.831 1.408 1.382 1.0630.656 0.320 232  4 40 3988 −11 2945 20 110 1.731 1.236 1.309 0.935 0.6510.310 202  5 MCEC Na100 — 10 3213 −102 2640 −62 77 2.359 2.145 1.9031.730 0.602 0.340 409  6 20 2750 −50 2110 −18 95 2.226 1.855 1.600 1.3330.663 0.340 292  7 30 2206 5 1615 28 140 1.683 1.295 1.260 0.969 0.7920.330 194  8 40 2212 5 1530 39 150 1.686 1.204 1.204 0.860 0.800 0.320169  9 LCEC Na100 — 10 1828 −77 1612 −49 74 2.441 2.219 2.073 1.8850.592 0.340 454 10 20 1634 −15 1333 −1 105 1.967 1.639 1.677 1.398 0.6970.340 311 11 30 1650 −13 1180 45 115 2.000 1.538 1.444 1.111 0.710 0.330237 12 40 1386 −10 1130 59 140 1.700 1.214 1.290 0.921 0.768 0.320 18813 MCEC Na100 G20 10 8385 −305 7336 −224 33 2.510 2.282 2.195 1.9951.820 1.368 46 14 MCEC Na100 C10 10 10507 −497 9476 −425 26 2.636 2.3962.367 2.152 2.050 1.630 32 15 MCEC Na100 G20 20 7200 −245 6437 −162 392.218 1.848 1.955 1.629 1.700 1.223 33 16 HCEC Na100 G20 10 11808 −34810586 −260 29 2.588 2.352 2.459 2.236 1.727 1.368 53 17 LCEC Na100 G2010 7000 −280 6308 −211 32 2.597 2.361 2.391 2.174 1.789 1.368 51 18 LCECCa60Na40 G20 12 3909 −151 3363 −105 60 2.294 2.048 1.947 1.738 2.1681.355 28 19 MCEC Na100 KC110 10 6210 −125 5450 −79 29 2.225 2.023 1.9231.748 1.790 1.388 20 20 MCEC Ca50Na40 — 10 3593 −118 3138 −87 50 2.4222.202 2.075 1.886 0.915 0.610 209 21 MCEC K60Na40 — 10 3246 −100 2748−64 40 2.454 2.231 2.037 1.852 0.574 0.410 352 22 MCEC Mg60Na40 — 103750 −164 2930 −121 55 2.408 2.189 1.815 1.650 0.791 0.510 224 23 HCECCa60Na40 — 10 7016 −161 6388 −123 44 2.497 2.270 2.325 2.113 0.868 0.610240 24 LCEC Ca60Na40 — 30 1791 −31 1320 −4 113 1.969 1.515 1.480 1.1380.843 0.396 187 25 LCEC Ca60Na40 40 1658 −7 1207 18 138 1.798 1.2841.343 0.959 0.935 0.393 144 Na: Sodium Ca: Calcium K: Potassium Mg:Magnesium G: Gypsum C: Calcite KCl: Potassium Chloride

For the same CEC, lesser water content results in higher cohesiveenergy, but for same density/moisture, higher CEC crystallites achievemuch higher cohesive energy. As cohesion in clay particles are a resultof the hydrogen bonding between their surfaces and the water, morenumber of charge deficiency centers in higher CEC clay results in morenumber of hydrogen bonds and consequently raises the electrostaticattraction cohesive energy density. However, van der Waals repulsionsincrease due to the high vicinity of the crystallites. Therefore, highertotal CED mixes have corresponding higher repulsion van der Waals. Theseadditional repulsion forces play an important role in theexpansion/swell behavior of the clay particles in addition to thehydration by water molecules. Similarly, interaction with gypsum andcalcite also causes an increase in cohesive energy density due to theextra bonding created by the cations and anions. Although there is anincrease in repulsion due to van der Waals forces, increase inattraction forces due to electrostatic component has much higher valueand far outweighs the repulsion forces in these cases.

Natural expansive clay deposits usually form at deeper depths underconsolidation pressures from the overlying geological formations. Oncethese clay layers are exposed closer to the ground surface due toremoval of overlying layers, these layers become overconsolidated innature as a result of this stress relief. Moreover, fabric and structureof these clay deposits also change as a result of the stress relief andseveral other features, such as fissures and voids, develop in thestructure of these overconsolidated layers. To simulate the process ofoverconsolidation, compressed/compacted unit cells at higher pressureswere dynamically run in the Forcite module using Parrinello barostatunder a stress level of 1000 kPa. The pressure of 1000 kPa is a veryclose representation of the generally measured preconsolidationpressures of such deposits in the shallow subsurface. It is alsorepresentative of the compaction pressures of 1500 kPa used for thepreparation of laboratory samples. As a result of stress reliefsimulation, the unit cells achieved a lesser density due to more voidspace and the corresponding change in lattice spacing of the crystallitelayers. FIGS. 84 and 85 show typical unit cells before and after thestress relief simulation. Comparing the fabric before and after thestress relief shows not only an increase in pore space, but also anincrease in the d-spacing of the crystallites. CED results in FIGS. 76to 83 and Table 13 show a drop in cohesive energy as the structurerelaxed. There is also a decrease in the repulsion forces due to van derWaals. This drop is indicative of the elastic recovery of the soilstructure upon overburden stress relief.

Relaxed unit cell for each of the case under study was then sorbed withwater molecules. A typical water sorption of water molecules inNa-montmorillonite crystallites compacted with 30% water content isshown in FIG. 86. FIG. 86 shows that water molecules have occupied bothinter and intra crystallite space. For each phase of Sorption, 25,000steps were adopted to sorb the maximum number of water molecules.Depending on the initial water content, density, and other factors suchas cementation and exchangeable cations, water sorption for a singlestep varied from as low as 2% to maximum of 10%. Very low water contentis indicative of structure with very small pore space created either dueto high density or cementation. Higher water content sorption on theother hand indicates an open pore space fabric and high interlayerdeficiency. At the end of each sorption phase, the unit cell ofcrystallites were dynamically stabilized using Forcite module. Sorptionsteps were repeated in steps followed by stabilization through moleculardynamics until the swell cutoff was reached. Swell cutoffs have beendefined based on the cohesive energy concept and are explained below onswelling of water sorbed various forms of crystallites.

Each unit cell consisting of four crystallites and sorbed with themaximum number of water molecules in 25,000 steps in the Sorption modulewas subjected to molecular dynamics using Forcite module. The dynamicsmodule causes the movement of molecules to stable positions and resultin a stable expanded structure under a pressure of 1000 kPa (FIGS. 87and 88). It could be noted from FIGS. 87 and 88 that the volume changeoccurs both in the interlayer and intracrystallite space. The maximumexpansion occurs in the intracrystallite space while the interlayerspace continues to expand at slow pace until it reaches a maximum valueof about 17.5 Å.

From the cohesive energy density plots shown in FIGS. 76 to 81, it isnoted that each swelling phase causes reduction in cohesive energydensity at a uniform rate for each CEC of Na-montmorillonite except forHCEC at 10% water content. All the cases, except those with cementationand exchangeable cations other than Nat, a straight line plot betweenCED and water content is continued until it reaches a swell cutoff orterminal point. Swell cutoff points for all such cases were found to beterminating at a cohesive energy density of an order of 300 to 500J/cm³. By looking at the swell potential test results, terminal drydensities were found to be about 0.45 to 0.55 g/cm³ for 100% bentonitesamples. In the dynamics simulation, this density range has been foundequivalent to the cohesive energy density range of 300 to 400 J/cm³. Inthe absence of any other factor causing an early termination of swellingprocess such as cementation and/or exchangeable cations other than Na⁺,all the swell lines terminate at a cohesive energy density of 400 J/cm³.The termination points also indicate the terminal or post swell moisturecontent. For the other cases, terminal or swell cutoffs are discussedlater herein.

It could be observed from FIGS. 76 to 81 that terminal moisture contentfor high swell cases for each CEC is lesser than their low swellcounterparts. For instance, swell line for 30% initial water contentLCEC terminates at 113% while the one for 40% initial water content LCECfalls at 138%. A similar observation was also made during the swellpotential tests (Table 9); terminal moisture content for initialmoisture contents of 30% and 40% are 136% and 174% respectively. Thisanomalous phenomenon can be explained using the contribution of van derWaals to the cohesive energy density (FIG. 89). For these cases, inaddition to the expansion caused by water molecules, the repulsion forcedue to van der Waals results in pushing the particles apart. Since theseforces are higher in case of highly compacted specimens or lessermoisture contents, relatively higher swelling takes place at lower watercontent for such cases. The resulting swell potential determined fromthe swell simulations for all the cases under study are summarized inTable 13.

The most common types of cementation produced in natural soil depositsare by calcite, gypsum, and potassium chloride. From FIGS. 76 to 81, itcan be observed that there is a substantial increase in the cohesiveenergy density of an order of 20 to 300%. The CED contribution from vander Waals is repulsion in nature and is also higher than theircounterparts. For all these cases, unlike Na-montmorillonite, the plotbetween CED and moisture content is not a straight line. The plot has aninitial straight portion followed by a curvature and a straight line tothe terminal or swell cutoff. Swell cutoff for these cases have beendetermined to be the point up to cohesive energy density equivalent to4×10⁸ J/m³ plus CED difference between the specific case and itsNa-montmorillonite counterpart. FIGS. 80 and 81 show the typical curvedplots and the corresponding terminal or swell cutoff points and thecorresponding swell potentials are summarized in Table 13.

Several combinations of exchangeable cations shown in Table 12 weretransformed into respective unit cells and were simulated for swellingusing all the steps described above. FIG. 81 provides the correspondingcohesive energy plots for these various combinations. Replacing 60% ofexchangeable Na⁺ cation with K⁺ cation causes a reduction in swell byabout 15%, while 60% replacement with Ca and Mg²⁺ cations result in areduction by 50% and 45% respectively. These results also indicate thesensitivity of these models to the change in percent and type ofexchangeable cations. Bivalent cations such as Ca²⁺ and Mg²⁺ result inextra binding to the crystallite layers and hence cause a reduction inswell potential. Similarly, as compared to bivalent cations, monovalentK⁺ cation does not provide binding forces enough to cause substantialreduction in swell potential.

Based on the CEC and the type of major exchangeable cations, LCEC with60% Ca+40% Na could be considered as a close representative of thebentonite used in this study. Swell potential results of thiscombination very closely match the values obtained from swell potentialtests. Considering that some part of post swell water content resides inthe macro pores, the terminal moisture contents as assessed fromsimulations are also very close to the ones determined experimentally.

The results of the molecular level simulations of different CECs,moisture, density, exchangeable cations, and cementation effects werecompiled to form two unified sets of plots. One set of plots consists ofgraphs between two state variables i.e., water content and the total CEDfor all the possible variations of the parameters for each CEC (FIGS. 90to 93). Similarly, plots were prepared between CED and the third statevariable, swell potential, for the various cases considered in Table 13(FIGS. 94 and 95). In combination, these plots serve as a nano levelconstitutive model, a 3-D representation is provided in FIG. 95. Thesesurfaces can be used to determine the swell potential of any natural orcompacted expansive clays using the basic input parameters such asinitial moisture content, CEC, exchangeable cations, and totalcations/non-clay minerals.

The plots in FIGS. 90 to 93 show a general trend of decreasing CED withthe water content until 30% and afterwards it remains almost constant.Any change in parameters like CEC, cementations, and cations, causes ashift in total CED and the shift remains constant throughout themoisture content range. To avoid cluttering of the data and for bettervisualization, several plots have been omitted in these figures.Development of an incremental form of constitutive relations is detailedlater herein.

In addition to the total swell potential determination, the molecularlevel simulation results for all the parameters such as CEC, watercontent, density, exchangeable cations, and cementation compounds havealso been used to develop the constitutive equations of a nano modelrelating the incremental intake water content to the correspondingchange in the volume as:d _(v)=(slope for straight line or hyperbolic for curved plots)d_(wc)  4-1

where

d_(v) and d_(wc) are change in volume and water content respectively

slope or slope change (hyperbolic)=(IDD−FDD)/(FWC−IWC)

IDD=initial dry density, FDD=final dry density, FWC=final water content,IWC=initial water content

A basic equation relating the initial water content and the totalcohesive energy density (TCED) is developed from FIG. 96 and isexpressed as:TCED=0.0625(IWC)³−3.575(IWC)²+10.5(IWC)+2830  4-2

Considering a constant shift in total cohesive energy density by changein exchangeable cations and by addition of cementing agents, equation4-2 has been modified as:TCEDm=0.0625(IWC)³−3.575(IWC)²+10.5(IWC)+2830+7100(C/0.1)+5050(G/0.2)+3010(KCl/0.1)+Ca(500)+Mg(300)+K(100)  4-3

where

TCEDm=modified TCED, Calcite, G=Gypsum, KCl=Potassium chloride,Ca=Calcium exchangeable cation, Mg=Magnesium exchangeable cation,K=Potassium exchangeable cation

Using this comprehensive relationship for total cohesive energy density,other required start and end points in the equation 4-1 could beobtained from the relationships developed from FIGS. 97 to 99. Thecorresponding relationships for Initial Dry Density (IDD), Final DryDensity (FDD), and Final Water Content (FWC) are provided below:IDD={−2E-15(TCED)⁴+5E-11(TCED)³−5E-07(TCED)²+0.0023(TCED)−1.5378}*1.85*(ABS(CEC-90)/90)  4-4FDD=−2E-22(TCED)⁶+5E-18(TCED)⁵−6E-14(TCED)⁴+3E-10(TCED)³−7E-07(TCED)²+0.0005(TCED)+0.3747  4-5FWC={1E-13(TCED)⁴−4E-09(TCED)³+4E-05(TCED)²−0.2037TCED+369.54}*ABS(CEC2-90)/CEC2*0.82  4-6

The constitutive surface shown in FIGS. 68 and 69 can be expressed inthe form of equations 4-4 to 4-6 to develop the equation for theconstitutive surface:Swell (%)=(FDD−IDD)FDD*100   4-7

Using the above equations of the nano model, swell potential wasdetermined for all the samples tested using swell potential tests in thepresent disclosure and are tabulated in Table 14. Similarly, swellpotential was also assessed for the undisturbed samples from the Easternregion of KSA tested by Hatneed and the results are tabulated in Table15 and plotted in FIG. 100. See Hameed, R. A. (1991), “Characterizationof Expansive Soils in the Eastern Province of Saudi Arabia”, MS Thesis,KFUPM, Dhahran, Saudi Arabia, July 1991, incorporated herein byreference in its entirety.

TABLE 14 Summary of comparison of swell potential tests results in thecurrent study and nano/molecular model predictions Nano Mois- SwellTests Model Prediction ture Initial Initial Final Final Final Sam- Con-Dry Wet Dry Wet Dry ple tent Ben- Gyp- Cal- Kao- Swell Density IMCDensity FMC Density Density Swell Density FMC No State NaM CaM toniteSand sum cite linite (%) (g/cm³) (%) (g/cm³) (%) (g/cm³) (g/cm³) (%)(g/cm³) (%) 1 Dry of — — 100 — — — — 184 1.290 29.5 1.67 136.0 0.45 1.07187 0.396 113 OMC 2 Wet of — — 100 — — — — 132 1.290 39.0 1.79 174.00.56 1.52 144 0.393 138 OMC 3 Dry of — — 60 40 — — — 153 1.577 19.5 1.8893.0 0.62 1.20 155 — — OMC 4 Wet of — — 60 40 — — — 111 1.577 26.0 1.99103.0 0.75 1.52 121 — — OMC 5 Dry of — — 30 70 — — — 89 1.750 11.3 1.9572.0 0.93 1.59 90 — — OMC 6 Wet of — — 30 70 — — — 53 1.750 18.8 2.0882.0 1.14 2.08 58 — — OMC 7 Dry of — — 10 90 — — — 32 1.917 5.2 2.0218.0 1.45 1.71 33 — — OMC 8 Wet of — — 10 90 — — — 5 1.917 13.4 2.1722.0 1.83 2.23 5 — — OMC 10 Dry of — — 30 60 10 — — 21 1.750 12.0 1.9656.0 1.45 2.26 28 1.355 60 OMC* 11 Dry of — — 30 40 30 — — 11 1.750 12.01.96 27.0 1.58 2.00 9 — — OMC* 12 Dry of — — 30 20 50 — — 6 1.750 12.01.96 19.0 1.65 1.96 6 — — OMC* 13 Dry of — — 30 40 — 30 — 74 1.750 12.01.96 80.0 1.01 1.81 32 1.63  26 OMC* 14 Dry of — — 30 20 — 50 — 68 1.75012.0 1.96 66.0 1.04 1.73 29 — — OMC* 25 NMC Qatif (Q-1) 29 1.367 7.21.47 55.6 1.06 1.65 28 1.355 60 *Static Compaction NMC: Natural MoistureContent IMC: Initial Moisture Content FMC: Final Moisture Content

TABLE 15 Summary of comparison of swell potential tests results fromHameed (1991) and nano/molecular model predictions Non-swell Non-swellSwell (%) Swell (%) cementitious cementitious from from Sample BH/TPDepth Smectite minerals associated Swell Nano No. Location No. (m) (%)(%) (%) tests* Model** 1 Al-Khars, Al-Hasa BH-9 2.5-2.7 7 50 3.5 2.2 4.72 Mahasen-Aramco, Al-Hasa BH-13  2.0-2.25 4 34 1.4 6.28 10.3 3Al-Hamadiya BH-11 1.0-1.3 8 35 2.8 7.16 11.0 4 Al-Salehiya BH-12 2.4-2.76 64 3.8 4.84 3.9 5 Al-Khars, Al-Hasa TP-7 1.1 6 39 2.3 8.4 8.4 6Al-Naathel, Al-Hasa TP-11 2.0-2.2 6 27 1.6 16.38 18.0 7 Mahasen-Aramco,Al-Hasa TP-11 2.0-2.2 4 32 1.3 13.11 14.2 8 Housing Area BH-1 3.8 30 4012.0 29 24.5 9 Housing Area BH-3 1.8-2.1 13 48 6.2 4.06 4.6 10 UmmAl-Sahek BH-6 0.45-0.6  25 32 8.0 14.35 13.0 11 Umm Al-Hammam BH-8 5.6-5.75 39 39 15.2 12.88 13.9 *Hameed (1991) **Current study

As observed from Tables 14 and 15, predictions of swell potential, finaldry densities, and moisture contents for most of the cases are veryclose to the values obtained from the macro level tests. It can also beobserved that major difference exists only in the measured and predictedvalues for samples with calcite as a non-clay mineral. This deviationcan be attributed to very low solubility of calcite in distilled wateras compared to gypsum that has a moderate solubility in water. Asdistilled water was used for the swell potential tests, very lowpercentages of calcite would have got interacted with the clay particlesconsequently causing only small reduction in swell potential. On theother hand, the molecular simulations for this case considers theinteraction of entire 10% calcite with the clay crystallite. Therefore,the extent of the percent of non-clay mineral interacting with claymineral in laboratory or natural samples should always be considered.

Minor deviations in some other cases could be attributed to thecontributions from the macro level features in the samples. So for thecases where macro features dominate in controlling the water in flow andthe volume change, it is required to consider the coupling of this nanomodel with micro and macro level models to assess the total swellpotential of the real fabric and structure of the expansive clays.

Application of the nano model to the natural soils requires a knowledgeof the quantity and distribution of the non-clay minerals in the matrix.This knowledge can be acquired from the XRD results and total cationsanalysis of these samples. Based on this close confirmation of swellpotential for undisturbed samples by nano model, it can also quiteeffectively be used for the assessment of swell potential of naturalexpansive clay deposits.

Using equation 4-1, typical plots showing swell versus water have beenplotted using straight line and hyperbolic variation in density andshown in FIGS. 101 to 103. FIG. 101 typically represents the swellbehavior of Na-montmorillonite without any other constraint and it showsa complete separation of particles at higher water contents. On theother hand, FIGS. 102 and 103 depict the volume change response ofexpansive clay minerals restrained by other factors such as additionalbinding from very high CEC, cementation from non-clay salts, and/orexchangeable cations other than sodium. These typical behaviors alsomark the validity of the developed model and the constitutiverelationships.

Among micro investigation techniques for the determination of the inputparameters in the molecular level simulations, powder XRD has providedvital information on the crystallite size and the relationship of thelattice (d-spacing) expansion with water content. Results from CT, FTIR,and ESEM are more qualitative in nature and provide complementaryinformation to XRD results.

Replacing part of the sand by calcite and gypsum in the swell potentialtest on bentonite/sand samples has resulted in substantial reduction inswelling as shown in Table 9. There is a reduction of 82%, 90%, and 95%in the swelling potential when 10%, 30%, and 50% gypsum was added toreplace the sand, respectively. There is also a reduction of 40% and 44%in swelling upon part of the sand being replaced by 30% and 50% calcite,respectively. The phenomenon of decrease in swelling by addition ofcalcite and gypsum might be resulting from the binding effects producedby these compounds to the individual or group of clay particles.

Although CEC and the percentage of smectite in the natural undisturbedsample of Qatif-1 is almost the same as of the commercial bentonite(30/70 sand-bentonite mix), the difference in percent swell is large,i.e., 29% vs. 121%. This difference might be closely attributed to thecementation effects provided by the calcite, gypsum, and other similarcompounds or salts present in the soil.

For the determination of the fundamental crystallite size from the XRDdata using Debye-Sherrer's method, various widths of the correspondingpeaks in the XRD data, removal of background, and leveling of the peakshave resulted in the assessment of the crystallite size in the range of59 to 108 Å. This knowledge has been used in the selection of the sizeof the crystallite in molecular level modeling.

XRD tests conducted on the specimens at various water contents conductedon the samples compacted on the dry and wet side of OMC indicated thatd-spacing of about 15 Å (equivalent to two water layers or 20% watercontent) exists in the clay crystallites on the dry side of OMC whiled-spacing of 17.5 Å occurs (equivalent to three water layers or 30%water content) on wet side of OMC. As the molding water content isrespectively 30 and 40% for the dry and wet side of OMC specimens, it isestablished that rest of the 10% water content for both the cases isadsorbed on the edges and ends of the crystallites. This fact has playeda key role in the assessment of the fundamental size of the crystallitein the molecular level simulation.

Owing to its micrometer level resolution, micro CT testing is limited inits use for the nano/molecular level studies. Therefore, in the presentdisclosure, micro CT has been used to visualize and evaluate only themicron level fabric of the pre and post swell samples using thecontrasting attenuation property of the clay particles before and afterthe swell test.

For the static compaction of the specimens to the modified Proctordensity in the Odometer rings, an equivalent static pressure has beendetermined as 1500 kPa. To achieve the modified Proctor density, astatic pressure of 1500 kPa could be used to compact the specimens intwo layers in the Odometer rings of 70 mm diameter and 19 mm height.

In addition to the exchangeable cations, total cations have also beendetermined for the natural and bentonite samples. Non-exchangeablecations, which are difference of these two, provide useful informationon the contribution of non-clay minerals in the soil to the molecularlevel volume change behavior.

In Sorption simulation in the Materials studio software, optimum numberof Monte Carlo steps to cause a realistic number of water moleculesadsorption have been determined to be 25000. After experimenting severalenergy cut off levels, 25000 steps cut off was adopted as the thresholdlimit for the realistic sorption. Simulation beyond 25000 steps resultedin the occupation of higher energy sites by water molecules andconsequently occurrence of an unrealistically high volume change.

For the simulation purpose, Metropolis Monte Carlo method has beenselected in the Sorption module of Materials Studio software. In thismethod, parameters selected for ratios of exchange, conformer, rotate,translate, and regrow have been selected as 0.39, 0.2, 0.2, 0.2, 0.2respectively, while the corresponding probabilities are 0.39, 0.2, 0.2,0.2, and 0.2. Amplitudes adopted for rotation and translation are 5° and1 Å respectively.

Universal force field, one of the force fields in-built in the MaterialsStudio software has been modified in this research. Several force fieldparameters in UFF such as atom types, atom typing rules, diagonal vander Waals, and generators were modified for Na, Ca, Mg, Al, and Si inthe light of the parameters suggested in CLAYFF force field. ModifiedUniversal force field has successfully been used for carrying outsorption and molecular dynamics simulations on clay minerals in thepresent disclosure.

Different confining or compaction pressures used to simulate the severallevels of geological and laboratory compaction pressures have shown thathigh pressures of an order of 1 GPa cause quick compaction and may beclosely representative of dynamic and static quick type of compactionusing the laboratory and field equipment. On the other hand, lowconfining pressures of an order of 0.01 to 0.1 GPa result in slowcompaction and hence might be simulating more closely slowcompaction/consolidation pressures for the geological deposits.

In the present disclosure, cohesive energy density (CED) has beenconsidered as an excellent indicator of the interaction of the soilstructure to the water sorption and the consequent volume change. CEDhas been found highly sensitive to various volume change variables suchas water content, density, CEC, type and percentage of exchangeable andnon-exchangeable cations.

A general trend observed in the present disclosure is that low CECcrystallites produced lesser CED, while higher CEC and the crystallitessorbed with other compounds showed higher values.

Total CED has been found to be increasing with increase in CEC, density,cementation, and bivalent cations and decreasing with water content,while van der Waals CED reduces and becomes repulsion in nature with thesame variation of the above parameters.

For the same CEC, lesser water content results in higher cohesiveenergy, but for same density/moisture, higher CEC crystallites achievemuch higher cohesive energy. As cohesion in clay particles is a resultof the hydrogen bonding between their surfaces and the water, morenumber of charge deficiency centers in higher CEC clay result in morenumber of hydrogen bonds and consequently raise the electrostaticattraction CED. However, at the same time, van der Waals repulsionsincrease due to the high vicinity of the crystallites. Therefore, highertotal cohesive energy mixes have corresponding higher repulsion van derWaals. These additional repulsion forces play an important role in theexpansion/swell behavior of the clay particles in addition to thehydration by water molecules. Similarly, interaction with gypsum andcalcite also causes an increase in cohesive energy density due to theextra bonding created by the cations and anions. Although there is anincrease in repulsion due to van der Waals forces, increase inattraction forces due to electrostatic component has much higher valueand far outweighs the repulsion forces in these cases.

All the combination cases, except those with cementation andexchangeable cations other than Na, a straight line plot between CED andwater content is continued until it reaches a swell cutoff or terminalpoint. Swell cutoff points for all such cases were found to beterminating at a CED of an order of 300 to 500 J/cm³. By looking at theswell potential test results, terminal dry densities were found to beabout 0.45 to 0.55 g/cm³ for 100% bentonite samples. In the dynamicssimulation, this density range has been found equivalent to the cohesiveenergy density range of 300 to 400 J/cm³. Therefore, in the absence ofany other factor causing an early termination of swelling process suchas cementation and or exchangeable cations other than sodium, all theswell lines terminate at a cohesive energy density of 400 J/cm³. Thetermination points also indicate the terminal or post swell moisturecontent.

For all the cases with cations other than Na and ones with non-clayminerals, plots between CED and moisture content is not a straight line.The plot has an initial straight portion followed by a curvature and astraight line to the terminal or swell cutoff. Swell cutoff for thesecases have been determined to be the point up to CED equivalent to 4×10⁸J/m³ plus CED difference between the specific case and itsNa-montmorillonite counterpart.

Terminal moisture content for high swell cases for each CEC is lesserthan their low swell counterparts. For instance, swell line for 30%initial water content LCEC terminates at 113% while the one for 40%initial water content LCEC falls at 138%. A similar observation was alsomade during the swell potential tests; terminal moisture content forinitial moisture contents of 30% and 40% are 136% and 174%,respectively. This anomalous phenomenon can be explained using thecontribution of additional expansion caused by the repulsion van derWaals forces. For these cases, in addition to the expansion caused bywater molecules, the repulsion van der Waal forces result in anadditional expansion. As swelling progresses, the repulsion force due tovan der Waals result in pushing the particles apart. Since these forcesare higher in case of highly compacted specimens or lesser moisturecontents, relatively higher swelling takes place at lower water contentfor such cases.

The results of the molecular level simulations of different CECs,moisture, density, exchangeable cations, and cementation effects werecompiled to form a nano model to determine the swell potential ofexpansive soils. Predictions of swell potential, final dry densities,and final moisture contents using the nano model have been found to bevery close to the values obtained from the macro level tests both forlaboratory control samples and undisturbed natural samples. Therefore,these constitutive surfaces and equations can be comprehensively usedfor the expansive soils with both clay and non-clay minerals and all thepossible combinations of CEC, water content, density, total cations, andexchangeable cations.

Molecular level models have been developed for the fabric and structureof both natural and compacted soils containing both clay and non-clayminerals. These molecular level models with the suggested parameters andprocedures can be used for any combination of clay minerals and otherinteracting compounds. These models can also be used to model the soilbehavior in other industrial fields such as pharmaceutical, agriculture,petroleum, and waste management.

The invention claimed is:
 1. A method of reducing the swell potential ofan expansive clayey soil comprising at least one expansive clay mineral,the proportion of the weight of the at least one expansive clay mineralrelative to the total weight of the expansive clayey soil being P_(ECM),the expansive clayey soil having a water content and a cation exchangecapacity (CEC) of from 30 to 250 meq/100 g of the expansive clay mineralon a dry basis, the method comprising: (a) carrying out aforcefield-modified molecular level simulation to determine an amount ofa swelling reduction agent to be incorporated into the expansive clayeysoil to form a swelling reduction agent incorporated expansive clayeysoil with a reduced swell potential S_(i(soil)) that is no greater thana pre-set level T*, wherein the swelling reduction agent incorporatedexpansive clayey soil comprises a swelling reduction agent incorporatedat least one expansive clay mineral having a swell potential representedby S_(i(ECM)) and S_(i(soil)) equals S_(i(ECM))×P_(ECM), wherein theswelling reduction agent comprises gypsum at a first weight percent ofthe amount of the swelling reduction agent, and at least one Mg²⁺exchangeable cation at a second weight percent of the amount of theswelling reduction agent, wherein the sum of the first weight percentand the second weight percent is no greater than 100%, wherein theforcefield-modified molecular level simulation comprises molecularmechanics, molecular dynamics, and Monte Carlo simulation techniquesconfigured to simulate the swell potential of the swelling reductionagent incorporated at least one expansive clay mineral S_(i(ECM)) basedon the water content as an initial water content and CEC of theexpansive clayey soil, the gypsum at the first weight percent of theamount of the swelling reduction agent, and/or the at least oneexchangeable cation at the second weight percent of the amount of theswelling reduction agent, and (b) incorporating the amount of theswelling reduction agent into the expansive clayey soil to form theswelling reduction agent incorporated expansive clayey soil.
 2. Themethod of claim 1, wherein the swelling reduction agent comprises thegypsum at the first weight percent of the amount of the swellingreduction agent, and wherein the forcefield-modified molecular levelsimulation comprises the steps of (i) a molecular level simulation ofwater sorption onto a crystallite of the at least one expansive claymineral to form a water sorbed crystallite of the at least one expansiveclay mineral with the water content of the expansive clayey soil as theinitial water content, (ii) a molecular level simulation of sorption ofgypsum in an amount proportional to P_(ECM)×the first weight percentonto the water sorbed crystallite of the at least one expansive claymineral, (iii) a molecular level simulation of assembling a plurality ofthe water sorbed crystallites of the at least one expansive clay mineralcomprising the swelling reduction agent to form a loose cubic unit celland at least one of a compacted unit cell at a first confining pressureand a stress relaxed unit cell at a second confining pressure less thanthe first confining pressure, wherein the loose cubic unit cell, thecompacted unit cell, and the stress relaxed unit cell each comprise Nwater sorbed crystallites of the at least one expansive clay mineralcomprising the swelling reduction agent and N is 2-8, and (iv) amolecular level simulation of water sorption onto and swelling of thecompacted unit cell at the first confining pressure or the stressrelaxed unit cell at the second confining pressure to form a swollencompacted unit cell or a swollen stress relaxed unit cell comprising theN water sorbed crystallites of the at least one expansive clay mineralcomprising the swelling reduction agent until a swell cutoff point isreached, wherein the extent of the swelling of the swollen compactedunit cell or the swollen stress relaxed unit cell comprising the N watersorbed crystallites of the at least one expansive clay mineralcomprising the swelling reduction agent at the swell cutoff pointcorresponds to the swell potential of the swelling reduction agentincorporated at least one expansive clay mineral S_(i(ECM)).
 3. Themethod of claim 1, wherein the expansive clayey soil further comprisessand and the method further comprises removing all or a portion of thesand from the expansive clayey soil prior to the incorporating theamount of the swelling reduction agent into the expansive clayey soil toform the swelling reduction agent incorporated expansive clayey soil. 4.The method of claim 1, wherein the expansive clayey soil furthercomprises sand and the method further comprises replacing all or aportion of the sand in the expansive clayey soil with at least onenon-expansive clay mineral prior to the incorporating the amount of theswelling reduction agent into the expansive clayey soil to form theswelling reduction agent incorporated expansive clayey soil.